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Biomedical subjects

R Strom

Publications and source records attributed to R Strom.

At least 127 records · Page 7Linked to original sources
PubMed1976

Octopamine plasma levels and hepatic encephalopathy: a re-appraisal of the problem.

An investigation on the blood levels of octopamine was carried out on 70 adult individuals. There was a statistically significant correlation between the levels of octopamine and hepatic encephalopathy. Normal subjects had values below 1 ng/ml, while patients with grade 3 or grade 4 encephalopathy constantly showed values above 3.2 ng/ml. In these two groups the distribution was fairly homogeneous. Through the differences between cirrhotics without neurologic involvement and those with grade 1 or 2 hepatic encephalopathy displayed statistical significance, distribution of values in these groups was rather non-homogeneous. Octopamine levels paralleled variations in mental state in 3 out 4 cases. No difference was found between venous and arterial values. The reaction of transmethylation used in the assay of octopamine was constantly found to be inhibited by the presence of plasma. This inhibition is probably due to the presence of one or more beta-hydroxyphenylethanolamines other than octopamine.

Adult↗
PubMed1976

Inactivation of Bacillus cereus beta-lactamase by halogenated isoxazolylpenicillins.

Upon preincubation with halogenated isoxazolyl-penicillins, the activity of Bacillus cereus beta-lactamase is decreased by a factor proportional to the inhibitor concentration. This inactivation, which concerns essentially the catalytic rate constant of the enzyme, occurs only at or above 37 degrees C with cloxacillin and dicloxacillin, and even at 25 degrees C with flucloxacillin. The dependence of the inactivation rate upon inhibitor concentration is consistent, in the former case, with the occurrence of a bimolecular reaction, and in the latter case, with a bimolecular process followed by a monomolecular step.

Bacillus cereus↗
PubMed1976

Enzyme defense against reactive oxygen derivatives. II. Erythrocytes and tumor cells.

The enzymatic destruction of oxidizing products produced during metabolic reduction of oxygen in the cell (such as singlet oxygen, H2O2 and OH radical) involves the concerted action of superoxide dismutase-which removes O-2 and yields H2O2-and H2O2 removing enzymes such as catalase and glutathione peroxidase. A difference in distribution or ratio of these enzymes in various tissues may result in a different reactivity of oxygen radicals. It was found that in red blood cells superoxide dismutase and catalase are extracted in the same fraction as hemoglobin, while glutathione peroxidase appears to be "loosely" bound to the cellular structure. This suggests that in red blood cells catalase acts in series with superoxide dismutase against bursts of oxygen radicals formed from oxyhemoglobin, while glutathione & peroxidase may protect the cell membrane against low concentrations of H2O2. On the other hand, catalase activity is absent in various types of ascites tumor cells, while glutathione peroxidase and superoxide dismutase are found in the cytoplasm. However, the peroxidase/dismutase ratio is lower than in liver cells, and this may provide an explanation for the higher susceptibility of tumor cells to treatments likely to involve oxygen radicals.

Acetylcholinesterase↗
PubMed1976

The interaction of the polyene antibiotic lucensomycin with cholesterol in erythrocyte membranes and in model systems. III. Characterization of spectral parameters.

The variations of optical density and fluorescence of lucensomycin are good indices of the binding of this polyenic antibiotic to membranes. The former parameter reflects more generally the binding to any site present in the membrane, while the latter is more specific for binding to cholesterol. The chromophore of the lucensomycin-cholesterol complex has a relatively long lifetime, is almost immobile in the membrane, and is not accessible to water-soluble fluorescence-quenching agents. The stoichiometry, evaluated fluorometrically, corresponds to about two cholesterol molecules per polyene. In colloidal cholesterol suspensions, the extent of binding as a function of free polyene concentration is described by rectangular hyperbolae, the dissociation constant being, however, dependent on the sterol concentration. In erythrocyte membranes, on the other hand, and even more markedly in model systems containing appropriate solvents, the combination between lucensomycin and the sterol sites is described by sigmoid titration curves, indicative of cooperative effects, and probably due to solvation of cholesterol.

Antifungal Agents↗
PubMed1973

The interaction of the polyene antibiotic lucensomycin with cholesterol in erythrocyte membranes and in model systems. I. A fluorometric and spectrophotometric study.

The increase of fluorescence emission of lucensomycin occurring upon interaction with cholesterol, either as colloidal suspension or included in phospholipid micelles or in erythrocyte membranes, was described. Colloidal cholesterol differed from that contained in membranes by the kinetic behavior of its interaction with lucensomycin, the reaction being very slow in the former case, very fast in the latter one. Variations of optical density also occurred, though neither the kinetics nor the titration curves were superimposable on those obtained fluorometrically. The stoichiometry was, however, the same.

Acetates↗
PubMed1973

The interaction of the polyene antibiotic lucensomycin with cholesterol in erythrocyte membranes and in model systems. II. Cooperative effects in erythrocyte membranes.

Fluorometric titration curves of erythrocyte membranes with increasing lucensomycin have a sigmoid shape. This behavior, which was not present when colloidal cholesterol suspensions were used, is, however, not peculiar to the membrane structure, being also present in cholesterol-containing phospholipid micelles. Addition of acetic acid induced or increased sigmoidicity. This behavior can either be due to a true cooperativity in binding or to different fluorescence yields of the various lucensomycin-membrane complexes. The latter hypothesis appears to be slightly favored.

Acetates↗