Search PubMed⌕ Search

Biomedical subjects

P Mandel

Publications and source records attributed to P Mandel.

At least 505 records · Page 28Linked to original sources
PubMed1975

Purification and studies on some properties of the 4-aminobutyrate : 2-oxoglutarate transaminase from rat brain.

Using various chromatographic procedures, 4-aminobutyrate : 2-oxoglutarate transaminase from rat brain has been purified 2400 times with respect to the initial brain homogenate. The purified protein, which has a specific activity of 10 mumol times min -1, x mg-1 gave a single band by acrylamide gel electrophoresis and isoelectric focusing. It has a molecular weight of 105000 +/- 5000 and an isoelectric point of 6.8. In the presence of 0.1% sodium dodecylsulphate, a single protein band is seen on polyacrylamide gel, corresponding to a molecular weight of 57000 +/- 5000. N-terminal analysis reveals two chains with the same N-terminal amino acid, thus the enzyme may be considered as a dimer consisting of two identical subunits. The pH optimum for enzyme activity is 8.5. Studies of the enzymic reaction show that the general mechanism is of the ping-pong bi-bi model. The Km for 2-oxoglutarate at saturating 4-aminobutyrate extrapolated to saturating 2-oxoglutarate concentration is 4 mM. 2-Oxoglutarate competitively inhibits the enzyme with respect to 4-aminobutyrate, with a Ki of 1.8 times 10(-4) M. The same phenomenon is seen for the reverse reaction where the Ki is 6.6 times 10(-4) M for succinic semi-aldehyde.

4-Aminobutyrate Transaminase↗
PubMed1975

Renal cortex guanylate cyclase. Preferential enrichment in glomerular membranes.

1. The localisation and some of the properties of rabbit kidney cortex guanylate cyclase (GTP pyrophosphatase lyase (cyclizing) EC 4.6.1.2) have been studied. Upon fractionation of dissociated renal cortex, guanylate cyclase activity was preferentially enriched in fractions of pure glomeruli, where its specific activity was 44.5 times that measured in tubular fragments. Most, if not all, of the glomerular activity was found to be firmly membrane-bound, whereas the guanylate cyclase activity of the tubules was mainly soluble. Therefore, particulate guanylate cyclase activity could serve as marker enzyme for kidney glomeruli. 2. All hormones or hormone-like agents tested were without effect on kidney guanylate cyclase activity. Triton X-100 stimulated both glomerular and tubular activity. 3. Considering the high cyclic GMP forming capacity of kidney glomeruli, part of the cyclic GMP found in urine might be synthetized locally in these structures.

Animals↗
PubMed1975

Phosphopeptide and phosphoprotein metabolism in brain.

Phosphopeptide and phosphoprotein phosphorylation was studied in rat brain microsomes and rat brain slices which were incubated in the presence of [gamma-32 P] ATP under various experimental conditions. Radioactive phosphoserine was isolated from phosphopeptides and phosphoproteins. Naplus, K+, Mg2+ and cyclic AMP had a stimulating effect on the labelling of phosphopeptides. Ouabain and Ca2+ lowered the level of 32P incorporation into the phosphopeptides. The phosphoproteins behaved similarly to the phosphopeptides except for the potassium effect. Chase experiments showed a faster decrease in the labelling of phosphopeptides than in phosphoproteins. We suggest that both compounds may be involved in active transport phenomena.

Adenosine Triphosphate↗
PubMed1975

[Barbiturate dependence at the cellular level].

In cultivated astroblasts of hamster, clone NN, increasing concentrations of sodium pentobarbital induce morphological changes in the sense of a cell differentiation. At the same time occurs a progressive dependence on the barbiturate, illustrated by cell degeneration when the effector is eliminated from the medium containing the cultivated cells.

Animals↗
PubMed1975

[Structural study of dopamine beta hydroxylase purified from human serum].

Dopamine-beta-hydroxylase (DBH) has been purified from human serum. The ensyme appeared to be pure as judged by the criterion of polyacrylamide gel electrophoresis. The native protein has a molecular weight of 250,000. When treated with dithiothreitor, the native protein could be dissociated into species with molecular weight of 64,500 and 32,000. It is suggested that the human circulating DBH is composed of four subunits and that each subunit may be composed of two polypeptide chains.

Dithiothreitol↗
PubMed1975

[Culture of dissociated cells from cerebral hemisphere of essentially neuronal make up].

Four methods are described to obtain pure neuronal cultures from chick embryo cerebral hemispheres. In our experimental conditions the proliferation of the glial cells in inhibited and cultures of either low or high neuronal density are obtained. The isolated neurons, however, did not survive longer than 8 to 10 days; the contact with glial cells seems to be necessary for the maintenance of the neurons in long-term cultures.

Animals↗
PubMed1975

Enzymatic synthesis of glucocerebroside by UDP-glucose: ceramide glucosyltransferase during ontogenesis of chicken retina.

The activity of uridine diphosphate-glucose: ceramide glucosyltransferase during chick retina ontogenesis was studied. This enzyme catalyzes the first step in the biosynthetic pathway leading to gangliosides. The glucosyltransferase activity was detected in 8 day old embryos, and was present in adult animals. The highest specific activity was found ca. day 10 of embryonic life. The radioactive product was identified as glucocerebroside by means of radiochromatography. The presence of phosphatidylcholine in the incubation mixtures was found to stimulate the enzyme.

Age Factors↗
PubMed1975

Human serum dopamine-beta-hydroxylase: purification, molecular weight, presence of sugars and kinetic properties.

1) Dopamine-beta-hydroxylase has been purified from human serum. Ammonium sulphate fractionation was used as the first step, the enzyme being precipated between 30 and 50 percent saturation. For the second step, the enzyme was adsorbed onto, and then eluted from a column of Concanavalin A covalently bound to Sepharose 4B. In the third step the enzyme was further purified by passage through two successive columns of Sephadex G-200. The final step, chromatography on DEAE-cellulose, gave a preparation of the enzyme with a specific activity of 36 mumoles of octopamine formed/30 min per mg of enzyme, representing a purification from the starting serum of 3,000 fold. 200 mug of enzyme could be obtained from 200 ml of serum. 2) The enzyme preparation was found to be pure or, at most, only slightly contaminated (depending on the starting serum) as judged by the criterion of polyacrylamide gel electrophoresis. 3) No cross-reaction could be observed between the human serum enzyme and rabbit antibody against bovine adrenal dopamine-beta-hydroxylase. 4) The molecular weight of the enzyme was found to be 250,000, i.e. less than the bovine adrenal enzyme. 5) Kinetic properties of the enzyme were studied. The mechanism of action of the enzyme was found to be similar to that of the bovine adrenal enzyme. Real kinetic parameters for both tyramine and ascorbate were calculated and found to be the same as those described for the bovine adrenal enzyme. 6) Interaction with Concanavalin A strongly suggests that the serum dopamine-beta-hydroxylase is a glycoprotein.

Ascorbic Acid↗