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S Meltzer

Publications and source records attributed to S Meltzer.

26 records · Page 2Linked to original sources
PubMed1984

Determination of coupling ratios of the calcium pump of sarcoplasmic reticulum by pulse methods.

Coupling of Ca2+ transport to ATP hydrolysis in isolated sarcoplasmic reticulum vesicles has been studied following pulsed additions of either ATP or Ca2+. ATP was infused as a pulse into medium, whose free Ca2+ concentration was maintained constant at saturating levels by a calciumstat procedure, using either a Ca2+-selective electrode or the spectrophotometric arsenazo III technique as Ca2+ indicators. The low ATP levels virtually exclude contributions by "basal" ATPase activity. Passive leakage of Ca2+, monitored after an ATP pulse, does not contribute more than 5% to subintegral coupling ratios. Pulsed additions of Ca2+ were made into medium. containing saturating concentrations of ATP, whose hydrolysis was monitored by a pH-stat procedure. Ca2+-stimulated hydrolysis continued until all the Ca2+ was transported into the vesicles. Values for the coupling ratio, Ca2+/ATP, of 1.82 +/- 0.12 and 1.79 +/- 0.15 were obtained by the ATP- and Ca2+-pulse methods, respectively.

Adenosine Triphosphate↗
PubMed1984

Effects of pH, temperature, and calcium concentration on the stoichiometry of the calcium pump of sarcoplasmic reticulum.

Coupling of Ca2+ transport to ATP hydrolysis by isolated skeletal muscle sarcoplasmic reticulum vesicles has been investigated by means of ATP pulse methods. The stoichiometric amounts of Ca2+ transported per pulse of ATP were measured by Ca2+-stat methods, using either a Ca2+ electrode or arsenazo III as end point detectors, or by means of 45CaCl2. Maximum coupling ratios (Ca2+/ATP), of 1.82 +/- 0.13 occurred at pH 6.8, 25 degrees C, and in the presence of saturating Ca2+ concentrations. Ca2+/ATP values decreased at alkaline pH, with an apparent pK alpha of 7.9. The coupling ratio was unaltered between 6 and 30 degrees C, but decreased to 0.4 at 42 degrees C. Uncoupling by alkaline pH and high temperatures was reversible. The coupling process was Ca2+-dependent, with a K0.5 value for Ca2+ of 0.12 microM and a Hill coefficient of 2.0. Ca2+ ions, which were transported into vesicles under conditions resulting in low coupling ratios, were retained as the calcium oxalate precipitate, following complete hydrolysis of substrate. Passive Ca2+ efflux and Ca2+ exchange, were independent of pH. The observed variations in Ca2+/ATP ratio cannot readily be explained on the basis of a pump-leak model. Rather, the Ca2+-ATPase appears to be capable of pumping Ca2+ ions, under physiological conditions, with variable stoichiometry that is dependent upon its thermodynamic loading.

Animals↗
PubMed1983

The effect of cardiotoxin on (Ca2+ + Mg2+)-ATPase of the erythrocyte and sarcoplasmic reticulum.

The effects of cardiotoxin on the ATPase activity and Ca2+-transport of guinea pig erythrocyte and rabbit muscle sarcoplasmic reticulum (Ca2+ + Mg2+)-ATPase (E.C.3.6.1.3) were investigated. Erythrocyte (Ca2+ + Mg2+)-ATPase was inhibited by cardiotoxin in a time- and dose-dependent fashion and inhibition appears to be irreversible. Micromolar calcium prevented this inhibitory effect. Specificity for (Ca2+ + Mg2+)-ATPase inhibition by cardiotoxin was indicated since a homologous neurotoxin had no effect. Cardiotoxin did not affect (Ca2+ + Mg2+)-ATPase activity from sarcoplasmic reticulum, but Ca2+-transport was 50% inhibited. This inhibition was not due to an increased Ca2+-efflux and could be the result of an intramolecular uncoupling of ATPase activity from Ca2+-transport. Inhibition of Ca2+-transport by cardiotoxin could not be prevented by millimolar concentrations of Ca2+. It is suggested that the biological effects of cardiotoxin could be a consequence of inhibition of plasma membrane (Ca2+ + Mg2+)-ATPases.

Animals↗
PubMed1980

[Precocious pseudo-puberty due to HCG-secreting androblastoma of the ovary. One case (author's transl)].

A case of ovarian androblastoma (arrhenoblastoma) of the intermediate differentiation type in a 5-year old girl is reported. The clinical features were precocious isosexual puberty with secondary masculinization. The tumour was removed but relapsed 26 months later, requiring ovariectomy and salpingectomy. The patient, who has now been followed up for 7 years and 6 months, is definitely cured. Biochemically, the androblastoma was accompanied by high plasma levels of oestrogens, androgens and, quite exceptionally, human chorionic ganodotropin, alpha HCG and beta HCG. Light and electron microscope examination failed to differentiale Sertoli cells from granulosa cells and Leyding cells from luteinized ovarian stroma cells. Areas resembling syncytiotrophoblastic cells were very limited and could not be seen under the electron microscope. Some cells looked like undifferentiated germ cells. The HCG secreted was biologically active on rabbit ovaries (Reiprich's reaction) but inactive on the girl's contralateral ovary, which was found on two biopsies to be unstimulated and prepubertal.

Adolescent↗
PubMed1961

The nitrogenous constituents of the lipids of several dog tissues.

A technique is described for the resolution and quantitative determination of the nitrogenous constituents of dog tissue lipids. Results of representative analyses are presented for seven different tissues. All but a few per cent of the total lipid nitrogen has been specifically accounted for as choline, ethanolamine, serine, other amino acids, ammonia, sphingosine, and hexosamine. Serine-containing lipids comprise a maximum of 2.6% to 7.7% of total lipid nitrogen of the tissues studied. Despite extensive purification of the lipid extracts, other amino acids and peptides are present in quantities comparable to serine. The ammonia content of the lipid hydrolyzates ranges from 4.3% to 5.9% of lipid nitrogen. From 1.0% to 9.4% of lipid nitrogen becomes water soluble after hydrolysis, and is neither choline, ammonia, nor primary amine. This is considered to be substituted amine, although no important fraction of this material has been identified.

Amino Acids↗