Direct enzymatic assay for reduced and oxidized glutathione.

A modification of a specific assay for the reduced (GSH) and oxidized (GSSG) species of glutathione is presented and compared with the method of Ellman (1959). The present method has an enzymatic basis using GSH as the specific cosubstrate for glutathione S-transferase activity. The enzymatic method resulted in comparable, but consistently lower, values for GSH and GSSG than did the method of Ellman. The greatest differences between the two methods occurred when measuring renal GSH and GSSG, possibly due to the presence of mixed thiols in the kidney. This enzymatic method was more specific and provided an accurate and reproducible method of GSH and GSSG determination.