Glutathione metabolism of the erythrocyte. The enzymic cleavage of glutathione–haemoglobin preparations by glutathione reductase

Abstract

A complex of haemoglobin and GSH was prepared by incubating haemoglobin with GSH and acetylphenylhydrazine. GSH could be released from the crude preparation by incubation with NADPH. However, when the haemoglobin preparation was separated from glutathione reductase by DEAE-Sephadex chromatography, NADPH no longer released GSH. Rather, the addition of a combination of either partially purified human erythrocyte or crystalline glutathione reductase and NADPH was required to release GSH from the haemoglobin–GSH complex. This complex is commonly believed to represent a mixed disulphide of GSH and the cysteine-β-93 thiol group. This interpretation was supported by the finding that prior alkylation of available haemoglobin thiol groups prevented the formation of the complex. By using haemoglobin–[35S]GSH complex as a substrate, it was shown that GSH itself released the radioactivity from the complex only very slowly. In contrast, the release of [35S]GSH was very rapid in the presence of NADPH and glutathione reductase. This suggests that the cleavage of the haemoglobin–GSH complex is not mediated by GSH with cyclic reduction of GSSG formed, but rather proceeds enzymically through glutathione reductase.