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At least 253 records · Page 14Linked to original sources
PubMed2006

Effective quenching of fragment formation in negative ion oligonucleotide matrix-assisted laser desorption/ionization mass spectrometry through sodium adduct formation.

Metastable decay of the sodium-free and the sodium adducts of the negatively charged hexameric nucleotides 5'-d(TTXYTT)-3' (X and Y are dC, dG or dA) in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS) is reported. We show that the sodium adduct formation may be used to quantitatively quench dissociation channels in oligonucleotide MALDI-MS, and we argue, that by means of effective steps in the sample preparation that lead to per-sodiation of the sample, the sample preparation and the mass resolution of oligonucleotide mass spectra in MALDI may be improved substantially. The dependency of the fragment formation on the degree of sodiation is also discussed in context with the underlying fragmentation mechanisms.

Anions↗
PubMed1981

Formation of striated muscle from myoblasts in vitro: inhibition of myotube formation by cis-4-hydroxy-L-proline and its reversal by native or denatured collagen (gelatin).

Previous efforts to define the nature of the complex requirements for the development of striated muscle in vitro led us to the finding that the presence of collagen in the extracellular environment is essential for the formation from myoblasts of the multinucleated myotube (1). In the present report we demonstrate that the proline analog, cis-4-hydroxy-L-proline, will inhibit myotube formation in vitro without affecting the aggregation of cells (fusion?). The presence of collagen or gelatin as a culture substratum overcomes the action of the analog. The role of collagen in the development of the myotube is discussed.

Animals↗
PubMed1976

A contribution to the formation mechanism of calcium oxalate urinary calculi. I. Stabilising urinary constituents in the formation of weddellite.

25 to 30% of calcium oxalate urinary calculi consist of the metastable Weddellite crystal phase. By fractionation of urine it was found that mineral substances are stabilising factors. The stability was checked in dry condition at room temperature at 38 degrees C and at 110 degrees C. These results could be confirmed by precipitation from synthetic solutions. Mg, Zn, Ni, Co, Mn and Cu individually, and above all in combination, promote the formation of Weddellite. The formation of mixed crystal phases must be considered one of the main factors for the stabilisation of Weddelite in the urinaty calculus.

Calcium↗
PubMed1978

Methemoglobin formation and binding to blood constituents as indicators for the formation, availability and reactivity of activated metabolites derived from trans-4-aminostilbene and related aromatic amines.

trans-4-Aminostilbene derivatives exhibit higher acute and chronic toxicity than 4-aminobibenzyl derivatives. Yet, trans-4-aminostilbene produced less methemoglobin in female Wistar rats than 4-aminobibenzyl. This cannot be explained by differences in N-oxidation since trans-4-nitrosostilbene was also less efficient than 4-nitrosobibenzyl. The fate of intravenously injected, highly and specifically 3H-labeled trans-4-aminostilbene, cis-4-aminostilbene, 4-aminobibenzyl, trans-4-nitrosostilbene and 4-nitrosobibenzyl was investigated. The results indicate that trans-4-aminostilbene and 4-aminobibenzyl are N-oxidized to a similar extent and primary activation products of trans-4-aminostilbene appear even faster in the blood. However, intermediates originating during methemoglobin formation are more reactive and covalently bind to hemoglobin 2--3 times as much with trans-stilbene as compared to bibenzyl derivatives. As a consequence the availability of these intermediates in the cyclic process and thus methemoglobin formation is reduced. Therefore, binding to hemoglobin rather than levels of methemoglobin appears to be an indicator for the availability and reactivity of some activated aromatic amine metabolites.

Animals↗
PubMed1994

Cytoplasmic granule formation in mouse pancreatic acinar cells. Evidence for formation of immature granules (condensing vacuoles) by aggregation and fusion of progranules of unit size, and for reductions in membrane surface area and immature granule volume during granule maturation.

We used a computer-assisted morphometry approach to analyze quantitatively the process of cytoplasmic granule formation in mouse pancreatic acinar cells stimulated with pilocarpine to induce secretion. Our findings suggest that each condensing vacuole/immature granule of pancreatic acinar cells is formed by the progressive aggregation of 106 to 128 "unit progranules" of narrowly fixed volume, define a range of 7.7 to 9.2 for the factor of volume condensation between the largest immature granules and the mature unit granule, and predict that the formation of a single mature unit granule by the aggregation and fusion of unit progranules involves a net reduction of at least 95% in the amount of membrane surface area associated with these structures.

Animals↗
PubMed1996

Potential contribution of optional urease-positive bacteria to idiopathic urinary calcium stone formation. II. Microlith formation kinetics in a fermenter model of the urinary tract infected by optional urease-positive microorganisms.

We investigated the effects of weak to moderate urease hydrolysis by optional urease-positive microorganisms in an artificial urine model enriched with calcium phosphate and calcium oxalate in respect of calcium stone formation. The incubation experiments were performed using a discontinuously running fermenter device to simulate the urinary system. The kinetics of cell division rates, pH and ammonium ion production were measured and correlated to crystallite appearance in the incubation medium. Qualitative analyses of the sediments revealed apatite. Investigations using light microscopy and scanning electron microscopy (SEM) confirmed the matrix effect of bacterial glycoproteins. It was shown that initiation of calcium oxalate stone formation is in all probability equally determined by matrix effects and by heteronuclear crystallization if the urinary tract is infected by optional urease-positive bacteria. When urinary inorganic phosphate is present, calcium phosphate nidi are always initially formed, and may subsequently be coated by calcium oxalate.

Calcium Oxalate↗
PubMed1979

Intracellular mechanisms of the formation of homo- and heteropolymeric isozymes. I. Kinetics of the formation of the heteropolymeric isozyme of malate dehydrogenase in parasexual hybrids of two Acetabularia species.

The isozyme pattern of malate dehydrogenase (MDH) of Acetabularia crenulata and A. mediterranea is characterized by heterogeneity in different regions of the cytoplasm of both algae, as well as by species specificity. The formation of the heteropolymeric MDH isozyme is restricted to a definite region of the cytoplasm of heterokaryons and nuclear-cytoplasmic A.crenulata-A.mediteranea hybrids at different stages of their development. The data obtained suggest that the concentrations of the free subunits of MDH, coded for by homologous genes, are unevenly distributed in the cytoplasm of hybrid cells. The heteropolymeric MDH isozyme in these cells is presumably the result of the de novo synthesis of isozyme subunits. This seems plausible inasmuch as no exchange occurs between the homopolymeric MDH isozymes of both parental types in the cytoplasm. The formation of the heteropolymeric MDH isozyme is tentatively related to the spatial compartmentalization of the mRNAs of homologous genes coding for the MDH subunits.

Acetabularia↗
PubMed1986

Further characterization of brain 3,4-dihydroxyphenylethyleneglycol (DHPG) formation: dependence on noradrenergic activity and site of formation.

The dependence of brain and plasma 3,4-dihydroxyphenylethyleneglycol (DHPG) formation upon CNS noradrenergic neutronal activity was evaluated following manipulations that are known to alter the firing rate of the locus coeruleus (LC) neurons and as a consequence, noradrenaline (NA) release and turnover. In addition, the relative degree of intraneuronal formation of brain DHPG was assessed by studying the metabolism of released NA during uptake inhibition. Electrical stimulation of the LC for 20 min induced an increase in rat cortical (40-42%), hypothalamic (22-29%) and plasma (68-79%) total DHPG and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) levels. Two hours following administration of the alpha-2 adrenoceptor antagonist yohimbine (10 mg/kg, i.p.), rat brain cortical conjugated DHPG and MHPG as well as free MHPG concentrations were increased whereas cortical free DHPG levels remained unchanged. The same treatment also increased plasma total DHPG and MHPG levels. In mice given the NA uptake inhibitor desipramine (10 mg/kg, i.p.) 2 h prior to sacrifice, brain free DHPG and MHPG concentrations were significantly reduced by 30 and 40%, respectively, whereas yohimbine (1-20 mg/kg, i.p.) induced a dose-dependent increase in brain DHPG (60-80%) and MHPG (60-220%) concentrations. Pretreatment with desipramine (10 mg/kg, i.p.) 30 min prior to yohimbine reduced, in rat, or abolished, in mice, the yohimbine-induced elevation of brain DHPG levels. In contrast, desipramine augmented the effect of yohimbine on brain MHPG levels resulting in a shift to the left of the dose response curves. These findings indicate that brain and plasma DHPG levels are sensitive to changes in brain noradrenergic neuronal impulse flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Radiation induced formation of giant cells in Saccharomyces uvarum. II. Effect of X-rays on septum formation.

Thin sections of budding yeast cells and giant gells grown after X-irradiation have been examined by electron microscopy. The different steps of cross-wall formation during budding were documented with unirradiated cells. With X-ray induced giant cells cytokinesis was shown to be absent. Neither primary nor secondary septae appeared thus cell separation did not occur. Despite this fact both macromolecular synthesis and bud growth continued, giving rise to the formation of giant cells.

Cell Wall↗
PubMed1978

Polyethylene-glycol-mediated cybrid formation: high-efficiency techniques and cybrid formation without enucleation.

Polyethylene glycol (PEG) can be used to promote the fusion of enucleated cytoplasts from chloramphenicol (CAP)-resistant mouse cells with intact cells, resulting in the formation of viable cybrids. The techniques are simple and highly efficient, yielding up to one viable cybrid per 20 intact cells fused. It also seems that PEG can be used to induce cybrid formation without the necessity of prior enucleation of the CAP-resistant cells.

Animals↗
PubMed1985

The effect of aging on bone formation in rats: biochemical and histological evidence for decreased bone formation capacity.

Ectopic bone formation by subcutaneously implanted demineralized bone matrix powder (DBM) was assessed biochemically and histologically in Fischer 344 rats of different ages. The total calcium accumulated in implants was greatly depressed in older rats, as was the rate of 45Ca deposition. High alkaline phosphatase activity appeared later in the 10- and 16-month-old rats compared with 1-month-old rats, and the magnitude of the alkaline phosphatase activity was decreased in 16-month-old rats. The accumulation of the bone-specific vitamin K-dependent bone protein (bone gla protein, BGP) was decreased in the implants in older rats. Histological examination of the implants confirms the decreased ability of aged animals to produce bone in response to DBM. Measurements of total calcium, alkaline phosphatase, and BGP at the site of demineralized bone matrix implants clearly demonstrates that bone formation decreases dramatically with increasing age. Significant differences in total calcium can be detected even between 1-month-old and 3-month-old rats. Serum BGP shows a marked decrease (47%) between 1-month- and 3-month-old rats, a decrease not paralleled by a similar decrease in BGP present in calvarial or tibial bone.

Aging↗
PubMed1985

Octacalcium phosphate formation in vitro: implications for bone formation.

Octacalcium phosphate (OCP, Ca8H2(PO4)6 . 5H2O) has been found in kidney stones and dental calculi and proposed by Brown et al. [1] to be a precursor of hydroxyapatite in bone and teeth formation. As saliva and urine often have acidic pH which favors OCP formation, the question remains then whether OCP can form in the more basic extracellular fluid in the bone milieu. This paper shows that calcium phosphate crystal phases obtained from neutral and pH 7.4 solution mixtures containing [CaCl2] = 0.1-10.0 mM and [Na2HPO4] = 0.1-90.0 mM with 100-300 mosM at 37 degrees C include brushite (CaHPO4 . 2H2O), OCP, and hydroxyapatite (Ca5(OH)(PO4)3). In some solutions OCP transforms into hydroxyapatite after 1 or more days, but brushite has not been observed to transform into OCP. Assuming the extracellular bone fluid has [Ca2+] = 1.0 mM, 300 mosM, and pH 7.4, this work suggests that hydroxyapatite crystals would only form when the ambient [Pi] greater than 5 mM, and that octacalcium phosphate may be a precursor.

Bone and Bones↗
PubMed2006

Prooxidant action of maltol: role of transition metals in the generation of reactive oxygen species and enhanced formation of 8-hydroxy-2'-deoxyguanosine formation in DNA.

Maltol (3-hydroxy-2-methyl-4-pyrone) produced reactive oxygen species as a complex with transition metals. Maltol/iron complex inactivated aconitase the most sensitive enzyme to oxidative stress. The inactivation of aconitase was iron-dependent, and prevented by TEMPOL, a scavenger of reactive oxygen species, suggesting that the maltol/iron-mediated generation of superoxide anion is responsible for the inactivation of aconitase. Addition of maltol effectively enhanced the ascorbate/copper-mediated formation of 8-hydroxy-2'-deoxyguanosine in DNA. Oxidation of ascorbic acid by CuSO(4) was effectively stimulated by addition of maltol, and the enhanced oxidation rate was markedly inhibited by the addition of catalase and superoxide dismutase. These results suggest that maltol can stimulate the copper reduction coupled with the oxidation of ascorbate, resulting in the production of superoxide radical which in turn converts to hydrogen peroxide and hydroxyl radical. Cytotoxic effect of maltol can be explained by its prooxidant properties: maltol/transition metal complex generates reactive oxygen species causing the inactivation of aconitase and the production of hydroxyl radical causing the formation of DNA base adduct.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1984

Pyruvate formate-lyase (inactive form) and pyruvate formate-lyase activating enzyme of Escherichia coli: isolation and structural properties.

The catalytically active form (Ea) of pyruvate formate-lyase in Escherichia coli cells is generated from an inactive form of the enzyme (Ei) through a post-translational process that requires a distinct activating enzyme and is linked to the cleavage of adenosylmethionine to methionine and 5'-deoxyadenosine. Ei and the activating enzyme were purified to homogeneity and structurally characterized. Ei has an alpha 2 oligomeric structure (2 X 85 kDa) and contains no cofactor. The amino acid composition has been determined. Out of a total of six cysteinyl residues per subunit, one shows an unusually fast reaction with iodoacetate (k2 = 7 (M-1 s-1) at pH 6.8, 30 degrees C), which is accompanied by loss of the activatability of the enzyme. The 1500-fold purified activating enzyme is a monomeric protein of 30 kDa. It contains a covalently bound, as yet unidentified chromophoric factor which has an optical absorption peak at 388 nm. Further studies of the in situ state of pyruvate formate-lyase detected a reversible backconversion of the active form Ea into Ei when anaerobic cells become nutrient-depleted.

Acetyltransferases↗
PubMed1984

Cell production and morphological pattern formation in primary brain cell cultures. I. Pattern formation within the basal layer(s).

Spontaneous pattern formation within the basal cellular layer of primary brain cell cultures were studied. Basal cells were found to be organized into a limited number of morphologically well distinguishable types of cell-arrangements. Phase contrast microscopy was used to characterize the different cell-assemblies morphologically. Under standard culture conditions the time of appearance and specific changes of relative frequency in time were also characteristic of different patterns. The distribution of mitotically active cells among the different morphological patterns within the basal layer was also investigated by recording [3H]thymidine uptake of cells. Reduction of mitotic activities of cells in the basal layer was found in the vicinity of overlying cells. In a given area of cultures the reduction of mitotic activity was proportional to the number of overlying cells. The influence of cell proliferation on the morphological pattern formation in primary cultures is discussed.

Animals↗
PubMed1994

A mutation blocking the formation of membrane or periplasmic endogenous and exogenous c-type cytochromes in Escherichia coli permits the cytoplasmic formation of Hydrogenobacter thermophilus holo cytochrome c552.

A mutant of Escherichia coli, JCB606, shown to be pleiotropically deficient in the formation of endogenous membrane and periplasmic c-type cytochromes, synthesised the apo form of the exogenous cytochrome c550 from Paracoccus denitrificans, but not the holo form. In contrast, a cytoplasmically located holo form of Hydrogenobacter thermophilus cytochrome c552 was found in E. coli JCB606. These findings support the proposition that the formation of the cytoplasmic H. thermophilus cytochrome c552 in E. coli does not involve the physiological pathway of c-type cytochrome biosynthesis in E. coli and that the haem insertion may be catalysed.

Cytochrome c Group↗
PubMed1990

Ca2(+)-dependence provides evidence for differing mechanisms of GABA-induced inositol phosphate formation and GABA potentiation of inositol phosphate formation induced by noradrenaline in rat cerebral cortex.

[3H]Inositol phosphate formation ([3H]IP) induced by gamma-aminobutyric acid (GABA) in slices of rat cerebral cortex prelabelled with [3H]inositol was abolished in Krebs-Henseleit medium without added Ca2+, but could be restored by addition of Ca2+. In contrast, GABA potentiation of noradrenaline-induced [3H]IP accumulation in the same tissue was still observed in the absence of added Ca2+. This provides evidence (a) that the effect of GABA alone on [3H]IP formation is indirect and (b) that the mechanism of this effect is unlikely to be the same as for the potentiation by GABA of [3H]IP accumulation induced by noradrenaline.

Animals↗
PubMed1984

Formation of mutagens in cooked foods. VI. Modulation of mutagen formation by iron and ethylenediaminetetracetic acid (EDTA) in fried beef.

Mutagen formation during frying of beef is inhibited by the heavy metal chelator ethylenediaminetetracetic acid (EDTA). The addition of 1% EDTA prior to cooking reduces the mutagenicity of the basic extracts to about 60% of control values. The addition of iron as ferrous chloride or ferric chloride at 10 ppm (approximately 50% of endogenous concentrations) doubles the mutagenic activity of beef extracts. Iron, which can be released by denaturation of heme protein, therefore, can modulate the formation of mutagens in beef during cooking.

Animals↗