Glutathione-insulin Transhydrogenase of Human Liver.

An enzyme which promotes the degradation of insulin has been isolated from beef liver (2, 3). This enzyme, which has been designated glutathione-insulin transhydrogenase (4), catalyzes the reductive cleavage of the disulfide bonds of insulin by a simple sulfhydryl compound such as glut,athione (4, 5). Because the process of degradation may be important in the etiology of diabetes mellitus, experiments were initiated to determine whether or not a similar enzyme exists in human liver. Ensinck, Coombs, Williams, and Valiance-Owen (6) have recently reported that B chain formed from insulin by the transhydrogenase binds to serum albumin, and that this bound B chain may be the synalbumin antagonist which has been proposed by Valiance-Owen et al. (7-9) to be present in excess in plasma of obese diabetics and prediabetics. The results presented in this paper show that the insulin-degrading enzyme, glutathione-insulin transhydrogenase, is present in human liver.