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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ATP-supported uptake of strontium by the fragmented sarcoplasmic reticulum is monophasic and proceeds more rapidly than the fast uptake of calcium. Strontium uptake is not activated by Pi. The accumulation of strontium is nearly proportional to the external strontium concentration even in the millimolar range. Internal and external strontium quickly equilibrate. One mole of strontium is stored for every mole of ATP split by the Sr2+-activated ATPase. In the absence of oxalate most of the strontium is taken up with a transport ratio of one. On the opposite, the transport ratio of calcium decreases immediately, especially when ADP is not instantaneously phosphorylated to ATP. In this case, energy conversion is uncoupled more effectively by the simultaneous action of ADP and free internal calcium, resulting in the interruption of the fast uptake. After depletion of ATP most of the stored strontium is released and the remaining fraction appears to be not exchangeable. Strontium activates the slow uptake of calcium, but reduces the amplitude of the fast uptake. The calcium induced release of strontium, and vice versa, is partial and transient. The strontium activated ATPase does not transport calcium at low ionic calcium concentrations.
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PMID:Comparison between strontium and calcium uptake by the fragmented sarcoplasmic reticulum. 13 46

Membranous vesicles (microsomes) were isolated from plasmodia of the acellular slime mold, Physarum polycephalum. The microsomes were about 0.2 about 0.2 micronM in diameter, and about 10 nm thick. The main protein component of the vesicles had a molecular weight of 100,000 daltons. Calcium ions were taken up by the microsomes only in the presence of Mg2+- ATP. The maximum amount of Ca2+ ions accumulated in the microsomes was 0.24 micronmole/mg protein. The Ca2+ uptake was not accelerated by oxalate. The ATPase [EC 3.6.1.3] activity required Ca2+ ions for full activation. The concentration of Ca2+ ions required for half-maximum activation was about 1 micronM. The Km and Vm values were 53 micronM and 1.6 micronmole/(mg-min), respectively. About 0.2 mole of Ca2+ ions was taken up by the microsomes, coupled with the hydrolysis of 1 mole of ATP. THE ATPase activity and Ca2+ uptake of the microsomes were not inhibited by sodium azide. Furthermore, electron microscopic examination showed that mitochondrial contamination was slight. These results suggest that a vesicular calcium transport system, analogous to the sacroplasmic reticulum in skeletal muscle, is involved in regulation of the Ca2+ concentration in plasmodia of Physarum.
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PMID:Uptake of calcium ions into microsomes isolated from Physarum polycephalum. 13 3

Membrane vesicles isolated from oxalate-grown cells of Pseudomonas oxalaticus accumulated oxalate by an inducible transport system in unmodified form against a concentration gradient. This accumulation was dependent on the presence of a suitable electron donor system such as ascorbate-phenazine-methosulphate. In the presence of this energy source, steady state levels of accumulation of oxalate were 10--20-fold higher than in its absence. The oxalate transport system involved showed a high affinity for oxalate (Km = 11 micron) and was highly specific. Oxalate transport was not affected by the presence of other dicarboxylic acids, such as malate, succinate and fumarate and only partly inhibited by acetate. The energy requirement for oxalate transport is discussed and it is concluded that this requirement is most likely equivalent to 1 mole of ATP per mole of oxalate.
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PMID:Active transport of oxalate by Pseudomonas oxalaticus OX1. 20 12

The oxalate content of urine is determined by means of oxalate oxidase and simple pH measurement. The enzyme specifically decarboxylates oxalate, producing two moles CO2 per mole oxalate. The CO2 diffuses into an alkaline buffer solution (Hallson, P. C. & Rose, G. A. (1974), Clin. Chim. Acta 55, 29--39) in the closed reaction vessel, and reduces the pH value, which is measured with an electrode. Only 125 microliter native urine is required to measure oxalate concentrations in the range of 80 mumol/l to 1.6 mmol/l (corresponding to 7 to 144 mg anhydrous oxalic acid per liter). The limit of detection is 10 nmol oxalate, and the accuracy is 101% with a coefficient of variation of 6%. The method described is insensitive to various interfering factors, such as reducing and oxidizing substances, cloudy or colored samples. It is therefore also suitable for oxalate determination in food technology and plant breeding.
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PMID:Determination of oxalate in urine using oxalate oxidase: comparison with oxalate decarboxylase. 46 68

The urinary excretion of calcium, magnesium, oxalate, creatinine, phosphate and urate was investigated in patients with urolithiasis and in normal subjects. The excretion of oxalate and urate per mole creatinine and the quotients calcium/magnesium, calcium X oxalate/magnesium and calcium X oxalate/(magnesium X creatinine) were significantly higher in stone formers than in normal subjects. The mean creatinine-correlated urinary excretion of calcium was higher and of magnesium lower in patients with urolithiasis, but the differences were statistically not significant. The urine investigation was supplemented with analysis of calcium, magnesium, creatinine, urate, bicarbonate and chloride in serum and a qualitative analysis of stone composition. A simple schedule for a biochemical grouping of patients with urolithiasis is presented and on the basis of the analytical findings it was possible to classify 67% of patients with so-called 'idiopathic stone disease' according to these principles.
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PMID:A biochemical basis for grouping of patients with urolithiasis. 66 34

Three structurally related substituted amino acids (N-compounds) were studied in a three-step dentin-bonding protocol. The first step of an acidic ferric oxalate solution and the third step of a surface-active comonomer were held constant throughout the study. In the second step, the amount of the N-compound--either N-phenylglycine (NPG), N-methyl-N-phenylglycine (NMNPG), or N-phenyl-beta-alanine (NPBA)--was varied in acetone from 0 mol/L through 5 x 10(-1) mol/L in seven steps. At 1 x 10(-3) mol/L for NPG and NMNPG, average bond strength values were 7.4 +/- 2.2 and 10.5 +/- 2.7 MPa. The highest bond strength value for NMNPG was at 1 x 10(-2) mol/L, with 13.2 +/- 4.0 MPa. The highest value for NPG was at 1 x 10(-1) mol/L, with a value of 11.8 +/- 2.5 MPa. The average bond strength for NPBA did not differ from zero across the entire range of concentrations. Molar efficiency was defined as the bond strength per mole of these applied N-compounds. For the two N-compounds that did provide adhesion to dentin, NPG and NMNPG, the average bond strengths rose, peaked, and fell as the amounts of applied N-compound were increased. The molar efficiency dropped off as the concentration of applied N-compound rose. The least operator-sensitive and most efficient N-compound, NMNPG, delivered a bond strength equivalent to that of NPG, with 10% of the applied NPG amount.
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PMID:Dentin-bonding molar efficiency using N-phenylglycine, N-phenyl-beta-alanine, or N-methyl-N-phenylglycine. 199 61

The roles of the phosphorylation (phosphorylated enzyme intermediate) and nucleotide binding domains in calcium transport were studied by comparing acetyl phosphate and ATP as substrates for the Ca2+-ATPase of sarcoplasmic reticulum vesicles. We found that the maximal level of phosphoenzyme obtained with either substrate is approximately 4 nmol/mg of protein, corresponding to the stoichiometry of catalytic sites in our preparation. The initial burst of phosphoenzyme formation observed in the transient state, following addition of either substrate, is accompanied by internalization of 2 mol of calcium per mole of phosphoenzyme. The internalized calcium is then translocated with a sequential pattern, independent of the substrate used. Following a rate-limiting step, the phosphoenzyme undergoes hydrolytic cleavage and proceeds to the steady-state activity which is soon "back inhibited" by the rise of Ca2+ concentration in the lumen of the vesicles. When the "back inhibition" is released by the addition of oxalate, substrate utilization and calcium transport occur with a ratio of 1:2, independent of the substrate and its concentration. When the nucleotide binding site is derivatized with FITP, the enzyme can still utilize acetyl phosphate (but not ATP) for calcium transport. No secondary activation of acetyl phosphate utilization by the FITC-enzyme was obtained with millimolar nucleotide. These observations demonstrate that the basic coupling mechanism of catalysis and calcium transport involves the phosphorylation and calcium binding domains, and not the nucleotide binding domain.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Roles of phosphorylation and nucleotide binding domains in calcium transport by sarcoplasmic reticulum adenosinetriphosphatase. 297 47

One reason that some people are prone to calcium oxalate nephrolithiasis is that they produce urine that is subnormal in its ability to inhibit the growth of calcium oxalate crystals. We have identified in human urine a glycoprotein (GCI) that inhibits calcium oxalate crystal growth strongly, and at low concentrations (10(-7) M); in this study, we have isolated GCI molecules from the urine of normal people and patients with calcium oxalate stones. GCI from stone formers is abnormal in three ways: it contains no detectable gamma-carboxyglutamic acid (Gla), whereas normal GCI contains 2-3 residues of Gla per mole; about half of the GCI in urine of patients inhibits crystal growth 4-20 times less than normal GCI as judged by its performance in a kinetic growth assay, in vitro; at the air-water interface, patient GCI has a film collapse pressure approximately half of normal. GCI molecules from the urine of patients with calcium oxalate nephrolithiasis are intrinsically abnormal, and these abnormalities could play a role in the genesis of stones.
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PMID:Urine glycoprotein crystal growth inhibitors. Evidence for a molecular abnormality in calcium oxalate nephrolithiasis. 405 37

Urinary excretion of calcium, magnesium and oxalate was studied in 38 patients with urolithiasis on two different occasions, and there appeared to be a good correlation between the biochemical findings in the two samples. All values were expressed per mole of creatinine and it was furthermore demonstrated that the variation in creatinine excretion was considerably less than the variation in urine volume. The calcium/magnesium quotients were calculated in 113 2-hour fasting urine samples and 24-hour urine samples and a good correlation was obtained. Biochemical grouping of the patients was performed by means of the two sets of values and the result obtained was approximately the same in both cases.
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PMID:Validity of biochemical findings in the evaluation of patients with urolithiasis. 735 65

Enrichment cultures of rumen bacteria degraded oxalate within 3 to 7 days in a medium containing 10% rumen fluid and an initial level of 45 mM sodium oxalate. This capability was maintained in serially transferred cultures. One mole of methane was produced per 3.8 mol of oxalate degraded. Molecular hydrogen and formate inhibited oxalate degradation but not methanogenesis; benzyl viologen and chloroform inhibited both oxalate degradation and methanogenesis. Attempts to isolate oxalate-degrading bacteria from these cultures were not successful. Oxalate degradation was uncoupled from methane production when enrichments were grown in continuous culture at dilution rates greater than or equal to 0.078 h-1. Growth of the uncoupled population (lacking methanogens) in batch culture was accompanied by degradation of 45 mM oxalate within 24 h and production of 0.93 mol of formate per mol of oxalate degraded. Oxalate degradation by the uncoupled population was not inhibited by molecular hydrogen or formate. Cell yields (grams [dry weight]) per mole of oxalate degraded by the primary enrichment and the uncoupled populations were 1.7 and 1.0, respectively.
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PMID:Characteristics of anaerobic oxalate-degrading enrichment cultures from the rumen. 742 29


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