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Biomedical subjects

M Vincent

Publications and source records attributed to M Vincent.

At least 397 records · Page 22Linked to original sources
PubMed1976

Effects of right atrial stretch on plasma renin activity.

In anaesthetized dog, right atrial stretch leads in the first five minutes to a decrease in plasma renin activity, when measured in inferior vena cava just above the renal veins. Bilateral cervical vagotomy increases plasma renin activity. After vagotomy, atrial stretch no longer has any effect on plasma renin activity. The results support the hypothesis of a control of renin secretion originating from atrial volume receptors.

Animals↗
PubMed1975

Mammalian 3-oxosteroid delta4-delta5-isomerase: a membrane-bound enzyme. I. Fluorescence study of the relationship between the enzymatic binding site, phospholipids, water and ions.

The microsomal membranes and the proteolipidic particles obtained by disruption of the microsomes by alkaline-earth ions at molar concentration have been compared by measuring the fluorescence properties of 1-anilino-naphthalene-3-sulfonate and naphthyl-1-phenylamine. The protein lipid arrangement of these two systems appears to be not essentially different. The study of fluorescence polarization of an hydrophobic probe (perylene) in function of Mg2+ concentration suggests a possible mechanism of disruption of the membrane by Mg2+ involving the strong structure-making effect of the ion. The comparison of the fluorescence polarization changes of perylene and equilenine (a competitive inhibitor of the isomerase) with the ionic concentration indicates that there is no direct relation between the bulk lipidic phase and the enzymatic binding site properties. Moreover, the emission of equilenine is completely quenched by I-, in contrast with the napththyl-1-phenylamine and perylene probes, which clearly demonstrates the accessibility of the catalytic site to water molecules and ions.

Anilino Naphthalenesulfonates↗
PubMed1975

Mammalian 3-oxosteroid delta4-delta5-isomerase. A membrane-bound enzyme. II. Activation by divalent cations.

Alkaline-earth ions (Mg2+, Ca2+ and Sr2+) have two specific effects on the kinetic parameters of the beef adrenal 3-oxosteroid delta4-delta5-isomerase activity in the microsomes and in the particles obtained after disrupting the membrane structure by action of 1 M MgCl2. On the microsomal enzyme, a 2-fold increase of V is observed with the three cations under study. The small difference in the effect of the three ions could be related to their hydration energy. It is suggested that the interaction of the ion with water is the determinant step of the activation mechanism and not the fixation of the ion on the enzyme or on some others possible binding sites in this system. With the enzyme in the proteolipidic particles, the use of EDTA as a chelating agent for the cations present in the enzymatic assay, allows the characterization of two effects: at low concentration of EDTA, an increase of Km is observed and at higher concentration (2 mM), V is decreased. A subsequent addition of Mg2+ leads to an activation in two steps: V is increased in the first step without change in Km, the second step consists of a decrease of Km without any change in V. A relation between the structural perturbations induced by the ions (Gallay, J., Vincent, M. and Alfsen, A. (1975) Biochim. Biophys. Acta 397, 489-500) and their kinetic effect on the enzymatic reaction is established.

Adrenal Glands↗