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Biomedical subjects

A Kahn

Publications and source records attributed to A Kahn.

At least 523 records · Page 29Linked to original sources
PubMed1980

Purification of F4 phosphofructokinase from human platelets and comparison with the other phosphofructokinase forms.

The phosphofructokinase (ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) tetramers F4, F3L and F2L2 have been separated from human platelets, and purified to homogeneity by affinity chromatography on Dextran Blue-Sepharose 4B. The F subunits have a molecular weight of 85 000, identical to that of the M subunits. By contrast with L-type phosphofructokinase, the F-type enzyme seems to exist predominantly in a tetrameric form and not to aggregate to high molecular weight polymers. Specific activity of pure F4 phosphofructokinase is about 140 IU/mg of protein. Immunologically, it is easy to distinguish all the basic phosphofructokinase forms (i.e. M, L and F types); nevertheless a slight immunological cross-reactivity seems to exist between all these forms.

Blood Platelets↗
PubMed1980

Hereditary erythrocyte pyruvate-kinase (PK) deficiency and chronic hemolytic anemia: clinical, genetic and molecular studies in six new Spanish patients.

Clinical, familial and biochemical studies from six unrelated Spanish patients with hereditary hemolytic anemia and erythrocyte pyruvate-kinase (PK) deficiency are described. A remarkable molecular heterogeneity of mutant PK variants involving kinetic properties, molecular stability or electrophoretic mobility is demonstrated. In two patients whose PK variants showed abnormal electrophoretic pattern and strongly aberrant kinetic properties, a chronic hemolytic anemia associated with several other clinical manifestations of chronic hemolysis occurred. In patients whose PK variants showed less abnormal kinetic and electrophoretic characteristics, there was only moderate or mild hemolytic anemia. One patient's PK variant with no obvious kinetic or electrophoretic alterations, showed a markedly decreased heat stability with severe diminution of antigenic concentration of the enzyme. This patient presented a spectacular clinical and hematological improvement after splenectomy. The purpose of the present study is to describe six new PK variants of Spanish origin. In addition, an attempt is made to find relationships between molecular abnormalities of mutant PK variants and the severity of hemolytic anemia, in these patients. The possible role of some kinetic alteration, such as fructose disphosphate (FDP) activation or ATP inhibition of PK variants, in the clinical manifestations of chronic hemolysis is also suggested.

Adult↗
PubMed1980

Phosphorylation of human erythrocyte pyruvate kinase by soluble cyclic-AMP-dependent protein kinases. Comparison with human liver L-type enzyme.

Human red cell contain soluble adenosine-3',5'-phosphate-dependent protein kinases, which are able to phosphorylate the L' subunits of erythrocyte pyruvate kinase. Efficiency and maximum level of phosphorylation are very comparable in human liver and red cells. Phosphorylation of red cell pyruvate kinase results in the same kinetic modifications as for liver enzyme, namely a shift towards a 'T' allosteric state characterized by a decreased affinity for phosphoenolpyruvate and increased inhibition by the allosteric inhibitors ATP and alanine. In the course of red cell aging a small amount of partially proteolysed pyruvate kinase, devoid of the phosphorylatable site, appears; it resembles the subtilisin-treated L'4 enzyme and accounts for less than 20% of total pyruvate kinase subunits. Endogenous phosphorylation of pyruvate kinase from erythrocytes incubated in the presence of cyclic nucleotides produces the same kinetic modifications as phosphorylation in partially purified extract; this, however, does not change glucose consumption, lactate production and glycolytic intermediate concentrations of the incubated cells.

Cyclic AMP↗
PubMed1980

Phosphofructokinase in human fetus.

The isozymic composition of phosphofructokinase (EC.2.7.1.11) from human fetal tissues has been investigated by immunological characterization, electrophoresis, purification, and SDS-polyacrylamide gel electrophoresis of the dissociated subunits. One of the characteristics of fetal tissues is the indiscriminate expression by all the cells of two or three of the basic forms of phosphofructokinase without any isozyme really corresponding to a specifically fetal form. In particular, L-type enzyme, identical to the highly regulatory enzyme synthesized by the adult hepatocytes, is found in most fetal tissues, especially in muscle and brain. M-type subunits are also detected in most of the organs and constitute the major form in fetal muscle and adrenals. F-type subunits are predominant in fetal stomach and yolk sac and are practically the only form in fetal heart. Some electrophoretic and chromatographic differences between fetal and adult M-type phosphofructokinase exist; whether their nature is genetic or posttraductional is so far unknown. Some differences (of molecular weight and chromatographic properties) are also detected between the fetal L-type subunits and enzyme from adult granulocytes. A mild proteolytic attack of the former by subtilisin transforms it into an enzyme form indistinguishable from granulocyte phosphofructokinase.

Adrenal Glands↗
PubMed1980

Hormone receptors.

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Catecholamines↗
PubMed1980

Arthritis.

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Arthritis↗
PubMed1980

[Increased vascular permeability during endotoxinemia in the child (author's transl)].

There is no uniform agreement about the effects of bacterial endotoxins upon vascular permeability. We presently report some clinical observations indicating an increase in vascular permeability during sepsis and shock related to Neisseria meningitidis in children. 133 children, admitted for a severe infection due to Neisseria m. were separated into three groups according to the severity of the initial clinical picture. The patients presenting with a sepsis or shock had significantly lower mean plasma protein levels on admission. This was not related to any hemodilution or caloric deficiency. Hypoproteinemia worsened during the 24 first hours of treatment, despite hemoconcentration as presented by some patients [12]. The speed of decrease in protein concentrations was inversely related to the molecular weights of the different protein fractions. These observations indicate an increase in vascular permeability with maintainance of vascular membrane selectivity to macromolecules during early meningococcic septicemia and shock.

Blood Proteins↗
PubMed1979

The permeability coefficient of albumin of the isolated rat mesentery. Modification by some mediators of inflammation, cyclic AMP and calcium.

In order to study the mechanisms whereby mediators of inflammation exert their exudative effects, we used isolated rat mesentery placed as a separation membrane between the two compartments of a diffusion cell. In this experimental arrangement, the permeability coefficient of albumin (PA) can be easily computed from the equilibration rate of 125I-labelled albumin added to one compartment. Histamine, bradykinin, serotonin and prostaglandins A1, A2, E1, E2, F1 alpha and F2 alpha all increased PA to some extent, the maximal values being approx. +60%. Dibutyryl-cyclic AMP, theophylline and isoproterenol also increased PA, thus suggesting involvement of cyclic AMP. Direct measurements of this nucleotide confirmed this hypothesis; furthermore, a linear relation between cyclic AMP levels and PA could be demonstrated. In contrast, cyclic GMP is probably not involved in the control of PA. Calcium-depleted tissues had a low PA (approx. 40% below controls), and did not respond to exogenous prostaglandin E1. These results suggest that transmesenteric passage of albumin is at least partly controlled by cyclic AMP and intracellular Ca2+ levels.

Animals↗
PubMed1979

G6PD deficiency with Gd(-)A like variant in a Chinese family from Cambodia.

A low rate value of G6PD was found in red blood cells from a Cambodian boy. Enzyme mapping was performed according to the WHO standard methods. G6PD presented all the characteristics of the A(-) variant encountered in the Negroes and behaved distinct from fast migrating enzymes described in China. No negro was in the ancestry of the mother.

Adult↗