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PubMed1983

Fluoride, hydrogen, and formate activate ribulosebisphosphate carboxylase formation in Alcaligenes eutrophus.

Alcaligenes eutrophus formed ribulosebisphosphate carboxylase (RuBPCase; EC 4.1.1.39) when grown on fructose. Addition of sodium fluoride (NaF) to fructose minimal medium resulted in a slightly decreased growth rate and a rapid fivefold increase in RuBPCase specific activity. With citrate, a glucogenic carbon source, RuBPCase was also formed, However, addition of NaF to cells growing on citrate resulted in a 50% decrease in RuBPCase specific activity. Among the enzymes of fructose catabolism, NaF (10 mM) inhibited enolase in vitro by 98% and gluconate 6-phosphate dehydratase by 87%. Inhibition of the dehydratase by NaF was insignificant in vivo, as determined with a mutant defective in phosphoglycerate mutase activity. Growth of this mutant on fructose was not inhibited by NaF, and only a minor increase in RuBPCase activity was observed. From these results, we concluded that the product of the enolase reaction, phosphoenolpyruvate, played a role in RuBPCase formation. Addition of H2 or formate to the wild type growing on fructose or citrate did not affect the growth rate but resulted in rapid formation of RuBPCase activity. Mutants impaired in H2 metabolism formed RuBPCase at a low rate during growth on fructose plus H2 but at a high rate on formate. Apparently, additional reductant from H2 or formate metabolism induced RuBPCase formation in A. eutrophus.

Alcaligenes↗
PubMed1984

Relation between colony formation in calcium-deficient medium, colony formation in soft agar, and tumor formation by T51B rat liver cells.

T51B rat liver cells and several carcinogen-treated, carcinogen + saccharin-treated, or spontaneously altered clones of T51B cells were tested for their abilities to form colonies in calcium-deficient medium and soft agar and to produce tumors in athymic nude mice. Most (10 out of 11) of the clones which were derived from colonies in calcium-deficient medium were unable to form colonies in soft agar and 8 out of 11 were non-tumorigenic. Conversely, 6 out of 9 clones derived from colonies in soft agar were unable to multiply significantly in calcium-deficient medium and 5 of these 6 clones were also non-tumorigenic. Two of these 9 soft agar-growing clones were tumorigenic, one of which also proliferated in calcium-deficient medium, and the other of which acquired the ability to proliferate in calcium-deficient medium after it became able to form tumors in athymic nude mice. Thus, T51B rat liver cells gain the ability to grow in calcium-deficient medium and soft agar independently during the process of neoplastic transformation and neither characteristic by itself reliably predicts tumorigenicity.

Animals↗
PubMed1997

Cognitive bias in spider fear and control children: assessment of emotional interference by a card format and a single-trial format of the stroop task.

The aim of the study was to clarify whether fear in children is related to a distorted cognitive processing of fear-related information. In anxious children, only a few studies of this bias were performed which yielded inconsistent results. Martin, Horder, and Jones (1992. Cognition and Emotion, 6(6), 479-486) found a bias for spider words in spider-fear children, using a card format of the Stroop task. However, by using a single-trial format of the Stroop task, we previously found that both anxious and control children favored the processing of threatening information (Kindt, Brosschot, & Everaerd, 1997. Journal of Experimental Child Psychology, 64, 79-97). In the present study, we administered both a card format and a single-trial format of the Stroop task to spider-fear and control children. In line with our previous results, a bias for spider words was observed in spider fear but also in control children, regardless of the format used. Furthermore, the processing biases assessed by the two formats did not correlate, which suggests that they measure different mechanisms and/or that one or both mechanisms are unstable. It is speculated that certain cognitive developmental deficits in regulating emotions may be a vulnerability factor in the etiology of anxiety disorders.

Affect↗
PubMed1997

Temporal expression of PTHrP during endochondral bone formation in mouse and intramembranous bone formation in an in vivo rabbit model.

Expression of parathyroid hormone-related protein (PTHrP) messenger RNA (mRNA) and protein was investigated throughout the developmental progression of endochondral bone formation in mouse and intramembranous bone formation in an in vivo model in rabbit, using in situ hybridization and immunohistochemistry. Endochondral bone formation was investigated in a developing embryo, newborn, and adult mouse. In fetal long bones through to newborn (day 7), PTHrP mRNA and protein were consistently expressed in chondrocytes within the proliferative, transitional, and hypertrophic zones. In addition, high levels of PTHrP were also detected in osteoblasts on the surface of trabecular bone surfaces. Similarly, at the adult stage (week 7), PTHrP mRNA and protein were consistently expressed in chondrocytes at epiphyseal ends of the subarticular cartilage, within cortical periosteum, as well as in osteoblasts located at the metaphyseal trabecular bone surfaces. Using an in vivo intramembranous bone formation model in rabbits, expression of PTHrP mRNA and protein was demonstrated in preosteoblasts prior to trabecular bone formation (1-week bone harvest). As bone formed (2-, 3-, and 4-week bone tissue harvests), PTHrP mRNA and protein were highly expressed in actively synthesizing osteoblasts and in those osteocytes embedded within the superficial layers of the bone matrix. Lining osteoblasts and osteocytes buried deeply in the bone matrix displayed weak or no signal for PTHrP. The pattern of spatial and temporal expression of PTHrP demonstrated in cartilage cells and osteoblasts in the two systems suggests an important role of PTHrP in both endochondral and intramembranous bone formation.

Animals↗
PubMed1993

Triplex formation by oligodeoxyribonucleotides involving the formation of X.U.A triads.

The stabilities of oligodeoxyribonucleotide triplexes containing a single pyrimidine-purine base pair, which interrupts an otherwise purine-pyrimidine base pair motif, were studied by UV melting experiments. The oligomer systems consisted of an oligodeoxyribonucleotide target duplex d-GAAGAAAAAAYAAAA/d-TTTTZTTTTTTCTTC, I.II(Y.Z), or d-GAAGAAAAAGUGAAA/d-TTTCACTTTTTCTTC, IV.V(U.A), where Y.Z is C.G, T.A, or U.A and U is deoxyuridine. The third strand oligodeoxyribopyrimidine was d-CTTCTTTTTTXTTTT, III(X), or d-CTTCTTTTTCXCTTT, VI(X), where C is 5-methyldeoxycytidine. Triplexes were observed in the system III.I.II(X.C.G) when X was T or U. This may involve formation of T. or U.C.G triads in which the 4-carbonyl of T or U serves as a hydrogen bond acceptor for the N4-amino group of C. Triplex formation between III(X) and I.II(T.A) was only observed when X was G. In contrast to T.A or C.G, it appears a U.A base pair in the duplex target is a much more versatile participant in triad formation. Thus, stable triplexes were observed in III.I.II(X.U.A) and in VI.IV.V(X.U.A) when X was C, C, T, or U. The formation of a T.U.A or U.U.A triad can occur if the T or U of III translates approximately 1.4 A into the major groove, thereby allowing the 3-NH of T or U to donate a hydrogen bond to the 4-carbonyl oxygen of U in the duplex. Formation of C. or C.U.A base triads could involve formation of a single hydrogen bond between the third strand N4-amino group of C or C and the 4-carbonyl group of U of the target.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Composition↗
PubMed1975

Pyridine-2, 6-dicarboxylic acid (dipicolinic acid) formation in Bacillus subtilis. II Non-enzymatic and enzymatic formations of dipicolinic acid from alpha, epsilon-diketopimelic acid and ammonia.

Non-enzymatic formation of dipicolinic acid (DPA) from diketopimelic acid and ammonia was clearly demonstrated using a new method for DPA analysis. The reaction rates of DPA formation were almost the same under aerobic and anaerobic conditions. Nearly equimolecular quantities of DPA and tetrahydrodipicolinic acid were detected in spontaneous reaction mixture. The spontaneous reaction seemed to be due to dismutation of dihydrodipicolinic acid, resulting in DPA and tetrahydrodipicolinic acid. The apparent optimum pH of the spontaneous reaction was 8.2 and the maximal rate of DPA formation was observed with a 1 : 4 molar ratio of diketopimelic acid to ammonia. The rate of the spontaneous reaction was stimulated by ferrous sulfate, FMN, and riboflavin. Dihydrodipicolinate reductase catalyzes the reduction of dihydrodipicolinate, prepared from pyruvate and aspartic beta-semialdehyde, with NADPH as reductant. The reductase was isolated from Bacillus subtilis, and found to stimulate DPA formation from diketopimelic acid and ammonia. The enzymatic DPA formation was absolutely dependent on oxygen, and optimum pH was 6.4. The catalytic action of the enzyme was similar to that of the oxidase. Possible mechanisms of DPA formation from diketopimelic acid and ammonia are proposed.

Aerobiosis↗
PubMed1983

Cinnabarinate formation in malpighian tubules of the silkworm. Bombyx mori: reaction mechanism of cinnabarinate formation in the presence of catalase and manganese ions.

The formation of cinnabarinate in the presence of manganese ions and catalase was investigated spectrophotometrically. The absorption peak of cinnabarinate at 460 nm appeared only in a reaction system containing manganese ions and catalase. If catalase was omitted, a new absorption peak at 360 nm was observed while the absorption peak of cinnabarinate reached a plateau. Furthermore, in the presence of hydrogen peroxide, the absorption spectrum of cinnabarinate changed; catalase suppressed this absorption change. We conclude that in the course of cinnabarinate formation in the presence of manganese ions hydrogen peroxide is produced, which decomposes cinnabarinate. Catalase prevents the accumulation of hydrogen peroxide, which results in the steady increase of cinnabarinate. Cinnabarinate formation by manganese ions shows an initial lag phase. This lag phase disappeared by preincubating 3-hydroxyanthranilate under aerobic conditions. Incubation of 3-hydroxyanthranilate resulted in the generation of superoxide anions. When both manganese ions and superoxide anions were present, the lag phase of cinnabarinate formation disappeared. In the process of cinnabarinate formation, manganese ions serve to dismutate superoxide anions, as does superoxide dismutase; manganese (II) ions were oxidized to manganese (III) ions by superoxide anions. From these results we have proposed a mechanism of cinnabarinate formation catalysed by manganese ions.

3-Hydroxyanthranilic Acid↗
PubMed1991

[Studies on calcium oxalate crystal formation in urolithiasis. Multi-regressive analysis of urinary CaOx crystalline volumes and the effects of urinary various substances on CaOx crystal formation].

Because human urine contains various substances which can affect each other, it is quite difficult to clarify the mechanism of formation of calcium oxalate (CaOx) crystal in urine. The authors recently determined CaOx crystalline content and the concentrations of other substances in urine specimens from patients with urolithiasis and healthy volunteers, and subjected the data to multi-regressive analysis for the purpose of assessing the effect of these urinary substances on CaOx crystal formation. 1. In analysis of urine from patients with urolithiasis, the partial correlation coefficients of CaOx crystal formation with oxalic acid, sodium, calcium, uric acid magnesium were 0.67, 0.28, 0.18, and -0.10, respectively. The formula of regression was as follows: Amount of CaOx crystal (X 10(6) microns3/ml) = 3.59 X 10(-2) Ox (mM/L) + 4.72 X 10(-3) Ca (mM/L) + 4.52 X 10(-3) Na (mM/L) + 2.51 X 10(-4) UA (mM/L) -2.39 X 10(-2) Mg (mM/L) -1.65. The multiple correlation coefficient was 0.759. Thus, in patients with urolithiasis, urinary crystal formation was most dependent on the oxalic acid level, sodium, calcium, and uric acid were found to promote crystal formation, while magnesium to suppress it. 2. In analysis of urine from healthy volunteers, the partial correlation coefficients of CaOx crystal formation with oxalic acid and inorganic phosphorus were 0.51 and -0.24, respectively. The formula of regression was as follows: Amount of CaOx crystal (X 10(6) microns3/ml) = 1.91 X 10(-2) Ox (mM/L) -3.43 X 10(-4) P (mM/L) +0.29 The multiple correlation coefficient was 0.525.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1986

The pyruvate branchpoint in the anaerobic energy metabolism of the jumping cockle Cardium tuberculatum L.: D-lactate formation during environmental anaerobiosis versus octopine formation during exercise.

The cockle Cardium tuberculatum responds with a typical escape movement (jumping by foot contractions) when touched by a starfish. In addition, this species can survive anoxic conditions for up to 20 h at 22 degrees C. The maximum activities of various enzymes involved in energy metabolism were determined in foot, adductor muscle and gills. Three enzymes with pyruvate reductase activity (lactate-, octopine-, alanopine/strombine dehydrogenase) can possibly serve as the terminal step of anaerobic glycolysis. On the whole the activities of enzymes involved in aerobic metabolism are low. In whole specimens of C. tuberculatum the metabolic response to anoxic incubation, exercise and exercise following anoxia were investigated. During 15 h of incubation in oxygen-free sea water no significant change in the energy charge is observed. The levels of arginine-phosphate fall to 50% of the value in resting animals with a concomitant increase in arginine concentration, but virtually no formation of octopine occurs. D-lactate and alanine are the main end products of anaerobic glycolysis and accumulate to a similar extent during anoxic incubation. While D-lactate levels increase linearly with time, L-alanine exhibits a 2-h delay before concentrations begin to rise. There is little formation of succinate and no formation of propionate and acetate. Despite the remarkably high activities of the enzymes alanopine and strombine dehydrogenase only negligible amounts of alanopine are found after anoxia and no production of strombine occurs. Exercise results in a depletion of the arginine-phosphate stores, liberation of arginine and formation of octopine. In whole animals as well as in foot muscle these changes are closely correlated to the number of jumps performed. No accumulation of D-lactate, alanine and succinate was detected. Exercise after an anoxic preincubation period of 6 h results in a further depletion of the already diminished arginine-phosphate stores and formation of octopine as the only end product. During anoxia the contribution of glycolysis to the required energy is enhanced from 44% (after 2 h) to 86% (after 15 h). During exercise glycolysis contributes 36% of the energy demand but only 16% during exercise after anaerobic preincubation. Thus the direction taken at the pyruvate branchpoint can be predicted on the basis of the glycolytic flux. Octopine formation only occurs when the glycolytic flux is enhanced (during exercise at least 40-fold). At low glycolytic flux (60% reduction during anoxia) pyruvate is channelled to form D-lactate and alanine.

Alanine↗
PubMed1989

The molecular basis of granuloma formation in schistosomiasis. III. In vivo effects of a T cell-derived suppressor effector factor and IL-2 on granuloma formation.

Granuloma formation in schistosomiasis is characterized by the formation of a large lesion in acutely infected animals which subsequently decreases in size as disease progresses into the chronic phase. These in vivo studies confirm and extend previous in vitro observations on the regulation of granulomatous hypersensitivity by a T cell-derived suppressor effector factor (TseF). TseF regulation of granuloma formation in vivo and DTH are shown to be both antigenically and genetically restricted. This suppression is accompanied by a suppression of the ability of cells derived from TseF recipients to function in an in vitro assay of granuloma formation. Antigenic recognition, defined by cellular proliferation in response to antigenic stimulation, is uneffected by TseF administration. Administration of IL-2 reduces TseF function in acutely infected mice and results in increased liver granuloma size. However, the ability of cells derived from these animals to form granulomas in vitro is uneffected. Cells obtained from chronically infected IL-2 recipients do not produce TseF in vitro and granuloma size is increased in these animals. Animals receiving both IL-2 and TseF continue to demonstrate decreased granuloma formation, indicating that IL-2 does not effect the ability of preformed TseF to function. These observations suggest that TseF modulates granuloma formation in vivo and may interact with IL-2 in a dynamic process which determines the intensity of the granulomatous response.

Adjuvants, Immunologic↗
PubMedDate not supplied

Cytochrome P-455-nm complex formation in the metabolism of phenylalkylamines. VI. Structure--activity relationships in metabolic intermediary complex formation with a series of alpha-substituted 2-phenylethylamines and corresponding N-hydroxylamines.

The formation of cytochrome P-450 metabolic intermediary (MI) complexes from a homologous series of alpha-substituted 2-phenylethylamines and corresponding N-hydroxylamines was investigated during NADPH-dependent metabolism in liver microsomes from phenobarbital-pretreated rats. The alpha-alkyl substituent consisted of branched and unbranched alkyl chains ranging from 0-4 carbons and the benzyl group. All the compounds but 2-phenylethylamine generated the complex and double-reciprocal plots of the highest observed rate of complex formation vs. substrate concentration gave linear relations over a defined substrate range. The Vmax(obs) values for complex formation by the amines increased markedly with increasing size of the alkyl group and a good correlation was obtained between log Vmax(obs) and the logarithm of the octanol/buffer partition coefficient of the substrates. With the N-hydroxy compounds, complex formation was a much less selective phenomenon and without exception the rates were quite high with Vmax(obs) values as much as 100 times greater than those of the amines. The disappearance of substrate amines was independent of structure and at an initial substrate concentration of 100 microM about a 50% decrease was noted during a 20-min period in all cases. The results substantiate the previous notion that N-oxidation is a prerequisite for MI-complex formation from primary amines. The results also suggest that C- and N-oxidation have different rate-limiting steps and the microsomal enzymes catalyzing the N-oxidation seem to be deeply submerged in the lipid matrix, as amines with a low distribution are inactive or poor substrates for generating the cytochrome P-450 ligand. Also, it is evident that the MI complex formation does not impair the overall metabolism of the amines.

Animals↗
PubMed1998

Radiation-induced radical formation in beta-glycerophosphate single crystals studied by electron paramagnetic resonance and electron nuclear double resonance spectroscopy: formation of an allylic-type radical.

Single crystals of disodium beta-glycerophosphate pentahemihydrate (betaGP), Na2x(HO)CH2CH(PO(4)2-)CH2(OH)x5 1/2H2O, were X-irradiated at 77 and 280 K. EPR, ENDOR and FSE techniques were used to study the formation of free radicals in these irradiated crystals to characterize possible reaction mechanisms leading to dephosphorylation. Irradiation at 77 K reveals the presence of four different radicals: two alkoxy radical conformations, AR1 and AR2, (HO)CH2CH(PO(4)2-)CH2O. and two carbon-centered hydroxyalkyl radicals, LTR1, (HO)CH2CH(PO(4)2-) C.HOH, and LTR2, with a tentative structure (HO)CH2C.H(PO(4)2-)CH2OH. AR1 and AR2 were determined to be formed on each of the two independent molecules A and B of the asymmetrical unit of betaGP, each on the 3-end of the molecule. Irradiation at 280 K reveals the presence of three hydroxyalkyl allyl radicals, R1, R2 and R3, with the common chemical structure (HO)C.H-H=CH(OH). Radicals R1 and R2 are determined to form on molecules B and A of the asymmetrical unit, respectively. The site of radical formation for R3 could not be ascertained absolutely from the available data, and there is also evidence that suggests the possibility that R3 has a hydroxyphospho-allyl radical structure. Possible reaction mechanisms for the formation of both the 77 K radicals and the 280 K radicals are suggested and discussed. The formation of an allyl-type radical in such a small-molecule single-crystal model system is an interesting and surprising result which may be relevant to the formation of the so-called 3alphaH radical species commonly observed in irradiated solid cytosine nucleosides and nucleotides. The result is also important because of the formation of the hydroxyalkyl allyl radical in solid beta-glycerophosphate is at variance with mechanisms and products shown to dominate for this and similar systems in solution radiolysis.

Crystallization↗
PubMed1984

Anaerobiosis, formate, nitrate, and pyrA are involved in the regulation of formate hydrogenlyase in Salmonella typhimurium.

Three groups of mutants defective in the fermentative production of gas were isolated from Salmonella typhimurium LT2 subjected to transposition mutagenesis with Mu d(Apr lac). One group consisted of strains which lacked hydrogenase. The mutation site for this group was located in the vicinity of the known hyd gene. A second group consisted of mutants which lacked the formate dehyrogenase associated with hydrogenase. The mutation site was located in four of them. It was not in the vicinity of the previously described fhlD gene but was instead located at 93 min on the Salmonella map. The third mutant group, which consisted of strains that produced gas in triple sugar iron agar but not in nutrient agar supplemented with glucose, appeared to be pyrA mutants. The insertion site was located in the vicinity of pyrA , and they required arginine and pyrimidines for growth. Expression of the lac operon in the hyd mutants was induced by anaerobiosis. It was only slightly increased by the addition of formate under anaerobic conditions and slightly decreased by the addition of nitrate. Nitrate had no effect in an hyd ::Mu d strain that also carried a chlC::Tn10 insertion. Full expression of the lac operon in the fhl mutants required both formate and anaerobic conditions. The presence of nitrate in addition to formate resulted in activities about half those obtained in its absence, even in the fhl ::Mu d chlC::Tn10 double mutant. In the absence of formate, nitrate reduced expression only in the fhl ::Mu d single mutants. Expression of the lac operon among the pyrA mutants was repressed by arginine and cytosine and also by anaerobiosis. An explanation for the involvement of pyrA in aerobic and anaerobic energy metabolism is proposed.

Aerobiosis↗
PubMed1981

T lymphocyte colony-forming capacity of patients with immunodeficiency diseases: relationship of colony formation to E rosette formation and lymphocyte proliferation.

The formation of T lymphocyte colonies was studied in 30 normal subjects and 12 patients with suspected abnormalities in immune function. The mean number of colonies per plate in normal subjects was 1.159 +/- 411 which represented a plating efficiency of 0.5-1.0%. When individual cells from colonies of these normal subjects were studied for membrane markers, greater than 90% were E rosette-positive and less than 1% were positive for surface immunoglobulins. Blood lymphocytes obtained from all 12 patients showed diminished colony-forming capacity when compared to normal subjects with a range of 0-311 colonies. Six patients had less than 50 colonies/plate. Colony formation was diminished in some patients who had normal E rosette formation and lymphocyte proliferation in liquid culture. Because of these discrepancies it appears that colony formation is not a direct reflection of E rosette formation and lymphocyte proliferation. Evaluation of T lymphocyte colony-forming capacity may prove useful as an additional in vitro assessment of lymphocyte function.

Cell Division↗
PubMed1993

High-dose gestagens modulate bone resorption and formation and enhance estrogen-induced endosteal bone formation in the ovariectomized mouse.

To determine if gestagens of two separate classes have differing skeletal actions, we studied the effects of pharmacologic doses of norethisterone acetate (NETA), a 19-nortestosterone, and megestrol acetate (MA), a 17 alpha-hydroxyprogesterone, on bone formation and resorption in intact and in ovariectomized mice. In the same set of experiments, we also attempted to determine if these gestagens can alter the skeletal activity of 17 beta-estradiol (E2). Experimentally, the skeletons of 78 female BALB/c mice were prelabeled with [3H]tetracycline (3H-T). The animals were randomized to 13 groups of 6 mice each 3 days after the final 3H-T injection. Ovariectomies (OVX) were performed on 8 groups and sham operations (SO) on 5 groups. To study the skeletal effects of the gestagens, 4 groups each of the OVX and SO mice were treated with controlled-release pellet implants calculated to deliver 80 or 250 micrograms of NETA or MA per day. To study gestagen interactions with E2, 3 groups of OVX mice were treated with either 40 micrograms/day of E2 or 40 micrograms/day of E2 plus 250 micrograms/day of NETA or MA. One group of OVX and one group of SO animals received placebo pellets. Fluorochrome labels were administered 10 and 11 and 3 and 4 days before sacrifice to allow histomorphometric evaluation of bone formation. At the end of the 60 day protocol, tibiae and thoracic vertebrae were removed and processed for quantitating the levels of bone resorption based on the amounts of 3H-T retained in the bones. The femora were fixed and embedded for comparison of diaphyseal bone histomorphometry, and the humeri and lumbar vertebrae were prepared for bone density determinations. Reflecting an increase in bone resorption, 3H-T levels in tibiae and vertebrae were decreased in placebo-treated OVX animals compared to the placebo-treated SO group (p < 0.01). Treatment of both SO and OVX mice with NETA decreased bone resorption in a dose-dependent manner, but MA had no significant effects on vertebral bone resorption and increased bone resorption in the tibiae (p < 0.01). E2 treatment of OVX mice reduced bone resorption, but there were no significant interactions between the E2 and gestagen treatments on resorptive activity. Based on bone histomorphometry of in vivo fluorochrome labels, both gestagens increased periosteal bone formation rates but had no effect on endosteal bone formation (BFRe). In contrast, E2 treatment of the OVX mice stimulated bone formation at the endosteal surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗
PubMed1995

Competition for factors and cellular resources as a principle of pattern formation in Hydra. II. Assistance of foot formation by heads and buds and a new model of pattern control.

In Hydra long-range interactions between head, bud, and foot formation take place in addition to short-range interactions which are recognized as induction phenomena, occurring when transplants are placed into an environment of disparate positional value. Here the long-range promotion of foot formation is analyzed. The data show: (1) While head regeneration and the onset of budding are mutually inhibitory, in particular in Hydra vulgaris and strain reg-16 of Hydra magnipapillata, fully developed heads and advanced buds cooperatively support foot formation in both the bud and the parent. Utilizing these interdependences H. vulgaris can be caused to form ectopic feet and to regenerate feet at both ends of excised segments. (2) The foot-promoting activity returns late in head regeneration, as late as the apparent long-range "head inhibition" determined in transplantation studies. (3) While periodic treatment with diacylglycerol (DAG) increases the capacities to form heads and buds, the potency to form feet is transiently reduced. (4) When treatment with DAG is finished the elevated capacities to form heads and buds subside, in reg-16 and H. vulgaris there followed a phase of ectopic foot formation. (5) The foot does not promote head regeneration. Based on the results of this and previous studies the following hypotheses are proposed: (1) Heads and buds compete for resources, such as precursor cells and soluble head-promoting factors that are distributed in the interstitial spaces. (2) The ability to make use of these resources is associated with positional value and decreases down the body column. The decreasing capability is attributed to a decreasing complement of receptors for the head-promoting factors. (3) Feet are made by body regions which are the losers in the competition for these factors. (4) Superiority in the ability to compete for the locally available factors enables transplants to develop head structures, and inferiority causes them to form a foot. (5) Depletion of the head-promoting factors in the whole body column is a significant component of the "head inhibition potential" and mediates the assistance of heads and buds in foot formation. (6) A surplus of resources causes supernumerary head structures and delays or prevents foot regeneration. These interpretations have reference to a new receptor-based model of pattern control and are contrasted with prevailing hypotheses.

Animals↗
PubMed1997

Analysis of cell movement and signalling during ring formation in an activated G alpha1 mutant of Dictyostelium discoideum that is defective in prestalk zone formation.

Mound formation in the cellular slime mould Dictyostelium results from the chemotactic aggregation of competent cells. Periodic cAMP signals propagate as multiarmed spiral waves and coordinate the movement of the cells. In the late aggregate stage the cells differentiate into prespore and several prestalk cell types. Prestalk cells sort out chemotactically to form the tip, which then controls all further development. The tip organises cell movement via a scroll wave that converts to planar waves in the prespore zone leading to rotational cell movement in the tip and periodic forward movement in the prespore zone. Expression of an activated G alpha1 protein under its own promoter leads to a severely altered morphogenesis from the mound stage onwards. Instead of forming a tipped mound, the cells form a ring-shaped structure without tip. Wave propagation pattern and dynamics during aggregation and mound formation in the mutant are indistinguishable from the parental strain AX3. However, at the time of tip formation the spiral waves that organise the late aggregate do not evolve in a scroll-organising centre in the tip but transform into a circularly closed (twisted) scroll ring wave. This leads to the formation of a doughnut-shaped aggregate. During further development, the doughnut increases in diameter and the twisted scroll wave converts into a train of planar waves, resulting in periodic rotational cell movement. Although biochemical consequences resulting from this mutation are still unclear, it must affect prestalk cell differentiation. The mutant produces the normal proportion of prespore cells but is unable to form functional prestalk cells, i.e., prestalk cells with an ability to sort out from the prespore cells and form a prestalk zone. Failure of sorting leads to an altered signal geometry, ring-shaped scroll waves, that then directs ring formation. This mutant demonstrates the importance of prestalk cell sorting for the stabilisation of the scroll wave that organises the tip.

Animals↗
PubMed1988

ATP formation onset lag and post-illumination phosphorylation initiated with single-turnover flashes. III. Characterization of the ATP formation onset lag and post-illumination phosphorylation for thylakoids exhibiting localized or bulk-phase delocalized energy coupling.

When 100 mM KCl replaced sucrose in a chloroplast thylakoid stock suspension buffer, the membranes were converted from a localized proton gradient to a delocalized proton gradient energy coupling mode. The KCl-suspended but not the sucrose-suspended thylakoids showed pyridine-dependent extensions of the ATP onset lag and pyridine effects on post-illumination phosphorylation. The ATP formation assays were performed in a medium of identical composition, using about a 200-fold dilution of the stock thylakoid suspension; hence the different responses were due to the pretreatment, and not the conditions present in the phosphorylation assay. Such permeable buffer effects on ATP formation provide a clear indicator of delocalized proton gradients as the driving force for phosphorylation. The pyridine-dependent increases in the onset lags (and effects on post-illumination phosphorylation) were not due to different ionic conductivities of the membranes (measured by the 515 nm electrochromic absorption change), H+/e- ratios, or electron transport capacities for the two thylakoid preparations. Thylakoid volumes and [14C]pyridine equilibration were similar with both preparations. The KCl-induced shift toward a bulk-phase delocalized energy coupling mode was reversed when the thylakoids were placed back in a low-salt medium. Proton uptake, at the ATP-formation energization threshold flash number, was much larger in the KCl-treated thylakoids and they also had a longer ATP formation onset lag, when no pyridine was present. These results are consistent with the salt treatment exposing additional endogenous buffering groups for interaction with the proton gradient. The concomitant appearance of the pyridine buffer effects implies that the additional endogenous buffering groups must be located on proteins directly exposed in the aqueous lumen phase. Kinetic analysis of the decay of the post-illumination phosphorylation in the two thylakoid preparations showed different apparent first-order rate constants, consistent with there being two different compartments contributing to the proton reservoirs that energize ATP formation. We suggest that the two compartments are a membrane-phase localized compartment operative in the sucrose-treated thylakoids and the bulk lumen phase into which protons readily equilibrate in the KCl-treated thylakoids.

Adenosine Triphosphate↗