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PubMed1986

Transient kinetics of formation of phosphorylated intermediate (EP) by fragmented sarcoplasmic reticulum from bullfrog skeletal muscle: ligand addition sequence-dependent rate of EP formation.

In order to obtain a better understanding of Ca2+-activated ATP hydrolysis by sarcoplasmic reticulum, the transient kinetics of phosphorylated intermediate (EP) formation was examined with different sequences of addition of Ca2+ and ATP to GEDTA-added (Ca2+-free) fragmented sarcoplasmic reticulum (FSR) from bullfrog skeletal muscle. With a short delay line (10-20 ms), the addition sequence of ATP followed by Ca2+ gives rise to a faster EP formation without any lag time. In the reverse sequence of ligand addition, a lag time of 2.5-3 ms was consistently observed irrespective of ATP concentration, and the rate of EP formation was lower. As the preincubation time with Ca2+ became longer, the rate constant for EP formation and the maximum level of EP attainable increased even in the presence of fixed concentrations of Ca2+ and ATP. The rate constant per the unit concentration of EP, however, remained constant, indicating second-order kinetics between Ca2+-activated FSR and ATP. With a preincubation time of 83.6 ms, no lag time was observed. In the addition sequence of ATP and 83.6 ms later Ca2+, a burst in EP formation was observed, which was followed by a usual exponential time-course of EP formation. Similar determinations in the presence of various concentrations of ATP led us to the following estimates of the rates of the reactions leading to EP formation at 15 degrees C. (formula: see text)

Adenosine Triphosphate↗
PubMed1981

Catechol estrogen formation by brain tissue: a comparison of the release of tritium from [2-3H]estradiol with [6,7-3H]2-hydroxyestradiol formation from [6,7-3H]estradiol by rabbit hypothalami in vitro.

In the course of establishing an assay for estrogen-2-hydroxylase activity, a detailed comparison was made between the formation of tritiated water (3H2O) and [6,7-3H]2-hydroxyestradiol (2-OHE2) by rabbit hypothalami in vitro from 2-3H- and 6,7-3H-labeled estradiol, respectively. The amounts of both 3H2O and [6,7-3H]2-OHE2 formed were stimulated several-fold by the nonionic detergent Tween-80. Maximum activity for both functions was associated with the soluble fractions (S2, 17,500 X g supernatant, for tritium release; S3, 100,000 X g supernatant, for 2-OHE2 formation). In contrast, maximal 3H2O formation by rat liver was associated with the microsomal (P3, 100,000 X g pellet) fraction and was virtually abolished by Tween-80. The amount of 3H2O formed exceeded, up to severalfold, the amount of 2-OHE2 produced under all conditions examined and in all subcellular fractions. The bulk of the excess 3H2O formation, unrelated to the production of 2-OHE2, could be eliminated by adding ascorbic acid (10 mM) to the incubation medium. However, a second, smaller component of spurious 3H2O release could not be suppressed. This component was responsible for a persistent lack of stoichiometry between the formation of 3H2O and 2-OHE2, with the former exceeding the latter by up to 2-fold. This discrepancy was unaffected by ascorbic acid (up to 20 mM), unlabeled 2-OHE2 (up to 10 microM), and reducing the temperature of incubation from 37 to 30 C, measures that prolonged the t1/2 of 2-OHE2 during incubation with hypothalamic tissue from under 3 min to over 100 min. These findings 1) raise doubts about the validity of using 3H2O formation from [2-3H]estradiol as a quantitative index of estrogen-2-hydroxylase activity, and 2) establish conditions under which further metabolism of 2-OHE2 is inhibited, thereby making it practical to quantify enzyme activity on the basis of the amount of catechol estrogen formed. Evidence is also presented that the release of 3H2O from [2-3H]estradiol by hypothalamic tissue, unrelated to 2-OHE2 formation, may be enzymatically mediated.

Animals↗
PubMed1990

[Effects of attitude formation, persuasive message, and source expertise on attitude change: an examination based on the Elaboration Likelihood Model and the Attitude Formation Theory].

The purpose of this study was to investigate how attitude change is generated by the recipient's degree of attitude formation, evaluative-emotional elements contained in the persuasive messages, and source expertise as a peripheral cue in the persuasion context. Hypotheses based on the Attitude Formation Theory of Mizuhara (1982) and the Elaboration Likelihood Model of Petty and Cacioppo (1981, 1986) were examined. Eighty undergraduate students served as subjects in the experiment, the first stage of which involving manipulating the degree of attitude formation with respect to nuclear power development. Then, the experimenter presented persuasive messages with varying combinations of evaluative-emotional elements from a source with either high or low expertise on the subject. Results revealed a significant interaction effect on attitude change among attitude formation, persuasive message and the expertise of the message source. That is, high attitude formation subjects resisted evaluative-emotional persuasion from the high expertise source while low attitude formation subjects changed their attitude when exposed to the same persuasive message from a low expertise source. Results exceeded initial predictions based on the Attitude Formation Theory and the Elaboration Likelihood Model.

Adult↗
PubMed1979

[Genetic control of the formation of plasmid F'. I. Effect of recA- and seg-2 mutations in an Hfr donor strain on the character of plasmid F' formation].

Assuming the similarity of the processes of illegitimate recombination, such as deletion formation, with the process of F' plasmid formation, we have undertaken the study of the influence of recA- and seg- alleles of Hfr donor on the F' plasmid formation. The data obtained demonstrate the strong influence of donor genotype on the frequency of F' plasmid formation and on the nature of F' plasmids formed, thus demonstrating that the most of F' plasmids have been formed via recombination in Hfr donor cells. The recA- mutation decreased the total yield of F' plasmids selected using both proximal and distal Hfr markers and affected drastically the distribution of the F' plasmids inheriting different proximal unselected markers. The existence of recA-dependent and recA-independent modes of F' plasmid formation was demonstrated. The Escherichia coli chromosome contains regions which involve preferentially in recA-dependent (between proA and gal, and clockwise from gal) or recA-independent (between leu and proA, and the region counterclockwise from argE) recombination. The seg-2 mutation causes only partial block of both recA-dependent and recA-independent recombination pathways, however it causes dramatic decrease of genetic exchanges leading to the formation of the type II F' plasmids. Both seg- and recA- mutations decrease the frequency of the formation of Tra+ F' transconjugants. The percent of Tra- transconjugants, which remain sensitive to MS2 and Q beta donor specific phages, also drops significantly under the influence of the recA- and seg- alleles. Thus, the recombination involving the F structure in wild type strains and seg- mutants occures preferentially in the points of F outside the regions essential for transfer and sensitivity to male specific phages, while in recA- and recA-ges- strains the points inside these regions (tra operon) frequently involved in F' plasmid looping out. There exist more strict correlation between the fertility and sensitivity to phage Q beta than to phage MS2.

Chromosome Deletion↗
PubMed1976

CO2 reduction to formate by NADH catalysed by formate dehydrogenase from Pseudomonas oxalaticus.

The direct reduction of CO2 to formate is catalysed by formate: NAD oxidoreductase in the presence of substrate amounts of NADH. Proof for this reaction is supplied by the detection of a CO2-dependent NADH oxidation, and by the identification of [14c] formate as the product of a NADH-dependent reduction of [14c]carbonate. The enzyme-catalysed CO2 reduction by NADH attains the equilibrium predicted by thermodynamic considerations, a state which is also reached from the formate side. The Michaelis constant for CO2 is about 40 mM indicating the low affinity of the enzyme for this substrate. The corresponding value for formate is 0.1 mM. Under the special conditions employed the enzyme catalyses the formate oxidation about 30 times faster than the CO2 reduction. That CO2 and not HCO3- is the active species in the reduction was shown by comparing the ph dependency of the velocities of the forward and back reactions and by observing the kinetics of CO2 reduction during the simultaneous attainment of the CO2-HCO3- equilibrium.

Aldehyde Oxidoreductases↗
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↗
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↗
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↗
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↗
PubMed1995

Early formation of DNA adducts compared with tumor formation in a long-term tumor study in rats after administration of 2-nitrofluorene.

2-Nitrofluorene (NF) is a model compound for nitroarenes which has been identified in diesel exhaust and in urban air. The current study was carried out to observe the carcinogenicity of different doses of NF to rats and DNA adduct formation in different organs at an early stage of NF administration. One group of rats was fed basal diet as a control, whereas the other three groups of rats were fed basal diet supplemented with different amounts of NF (0.24, 0.95 and 2.37 mmol NF/kg diet, referred to as low, medium and high dose, respectively). The rats were exposed to NF continuously for 11 months, after which all groups of rats were fed basal diet without NF for another 13 months. In the high dose group hepatocellular carcinomas were found in all rats (20/20), forestomach squamous carcinomas in 11 and cortical kidney carcinomas in 10 rats. Fifteen out of 19 rats fed the medium dose of NF had hepatocellular carcinomas, 16 had forestomach squamous carcinomas and 15 had cortical kidney carcinomas. The major tumors of the rats fed the low dose of NF were forestomach squamous carcinomas (10/18). DNA adducts formed in tumor target organs after 1, 2, 6 and 10 days NF administration were dose- and time-dependent. Ten days after the start of NF administration DNA adduct levels were found to be 54, 11 and 6 DNA adducts/10(8) normal nucleotides in forestomach, liver and kidney respectively. In the non-tumor target organs levels in the range 1.7-4.8 DNA adducts/10(8) normal nucleotides were found. DNA adduct formation in this study showed a good correlation with the localization of tumors, although there is a need for additional factors for tumor formation. The results indicate that DNA adduct formation is an important factor for tumor formation and suggest that DNA adducts could be used as biomarkers for genotoxic risk.

Animals↗
PubMed1991

HIV-induced syncytium formation requires the formation of conjugates between virus-infected and uninfected T-cells in vitro.

The transmission of HIV requires the interaction of the cell-surface CD4 receptor and the viral envelope glycoprotein. Experiments were performed to determine the role of other cell-surface molecules in the development of HIV-induced syncytia. Although CEM and MT-2 cells had similar cell-surface CD4 receptor densities, less than 1% of CEM cells and greater than 95% of MT-2 cells formed syncytia with H9 cells chronically infected with HIV-1 (H9-IIIB). When compared with CEM cells, MT-2 cells exhibited a 10-fold and threefold greater capacity to form homotypic and heterotypic conjugates with H9 cells, respectively. Increasing the conjugate formation capacity of CEM cells with the lectin wheat germ agglutinin led to a greater than 30-fold increase in the formation of syncytia with H9/IIIB cells. The formation of syncytia between MT-2 and H9/IIIB cells was magnesium-, energy-, temperature-, and actin-cytoskeleton-dependent, and could be inhibited (65%) by an anti-LFA-1 monoclonal antibody. The combination of anti-leukocyte function-associated antigen-1 (LFA-1) and anti-CD2 monoclonal antibodies resulted in a synergistic inhibition (89%) of syncytium formation. These results indicate that integrins and other cell-surface adhesion molecules regulate HIV-induced syncytium formation.

CD4 Antigens↗