Human plasma glutathione oxidation in normal and pathological conditions

Reduced glutathione added to human plasma disappears rapidly, and it is concomitantly recovered in its oxidized form. This oxidation is not due to the plasma metal content since it is not inhibited by EDTA or by passage of plasma through Chelex columns. Furthermore, this oxidation is not due to the peroxidase activity of glutathione S-transferases, which are usually undetectable in normal human serum, and it does not correlate with the amount of plasma glutathione peroxidase. A significant increase in the rate of glutathione oxidation was observed in plasma of patients with increased gamma-glutamyltranspeptidase activity. It is concluded that the side-oxidase activity of gamma-glutamyltransferase is responsible for the oxidation of glutathione in human plasma.