Les anomalies de la glycolyse au cours de l'anémie hémolytique par déficit du globule rouge en pyruvate kinase

Abstract

In two cases of hemolytic anemia with pyruvate kinase deficiency, we have studied the modifications of glycolysis in red blood cells and the kinetic behaviour of pyruvate kinase. Red cell glycolysis was markedly diminished. This alteration of the metabolic capacity coincides with an accumulation of phosphoenol pyruvate and phospho-glycerates and with a low level of hexose phosphates and triose phosphates. ATP content is very much decreased (35 % of normal values) ; 2,3-diphosphoglycerate is slightly increased. The level of pyridine nucleotides was found to be low, with predominance of reduced forms. These modifications are interpreted in relation to pyruvate kinase deficiency. The kinetic studies of the purified enzyme revealed two forms of pyruvate kinase in normal erythrocytes as well as in pyruvate kinase-deficient cells : — pyruvate kinase-B, with hyperbolic kinetics and K m app. (phosphoenol-pyruvate) = 3.6· 10 −5 M, insensitive to fructose diphosphate. — pyruvate kinase-A, with allosteric kinetics and K m app. (phosphoenol-pyruvate) = 19.3· 10 −5 M. The allosteric form is activated by fructose diphosphate at very low concentrations ( K m app. (fructose diphosphate) = 43·10 −9 M). In activated A-form, K m (phosphoenolpyruvate) is lowered at the same value as the B-form (= 2.8 · 10 −5 M). ADP is inhibitor at concentrations above 30 · 10 −5 M, and this action is overcome by fructose diphosphate. ATP inhibits at physiological concentrations. Pyruvate kinase-A and pyruvate kinase-B have identical V max and are interconvertible. The transition factors are discussed. In this study, no differences appeared in the molecular structure of pyruvate kinase in normal and deficient cells.