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  • Title: Influence of the rebox state of glutathione upon pyruvate kinase in the intact erythrocyte.
    Author: Sprengers ED, van Berkel TJ, Koster JF, Staal GE.
    Journal: Clin Chim Acta; 1977 Nov 01; 80(3):495-502. PubMed ID: 912917.
    Abstract:
    1. In isolated erythrocytes the ratio of reduced to oxidized glutathione was modified by the addition of diazinedicarboxylic acid bis-dimethylamide (diamide). Incubation of erythrocytes, with a decreased GSH/GSSG ratio, resulted in an increase in [S]0.5 of pyruvate kinase of phosphoenolpyruvate as measured in haemolysates. We presume this increase to be due to oxidation of the enzyme. 2. The apparent affinity of pyruvate kinase for phosphoenolpyruvate returned to normal when the GSSG formed was reduced to GSH intracellularly. Oxidation of pyruvate kinase could also be reversed by incubation of haemolysates with reducing agents such as 2-mercaptoethanol or dithioerythritol. 3. Intracellular oxidation of pyruvate kinase caused no significant changes in the Hill coefficient (n) or Vmax of the enzyme. However, the heat stability of the oxidized enzyme was lower than normal. Lability increased with increasing oxidation of the enzyme. 4. The possible role of oxidation processes in pyruvate kinase deficiency is discussed. It is concluded that not only 'in vitro' but also in the intact erythrocyte, pyruvate kinase is sensitive to oxidizing agents and intracellular redox state. However, that a decreased GSH/GSSG ratio can be a single cause of acquired pyruvate kinase deficiency seems highly improbable.
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