The occurrence of glutathione-insulin transhydrogenase in the retina

Insulin-degrading activity in the retina of cattle, rat, and rabbit has been studied. On the basis of activation by reduced glutathione, complete inhibition by N-ethylmaleimide, identification of one of the reaction products as the A chain of insulin, and reaction with antibody to purified beef pancreatic glutathione-insulin transhydrogenase, it is concluded that the insulin-degrading enzyme occurs in the retina. Preliminary studies showed that there is no difference in the levels of enzyme activity in retinal homogenates from cattle, rats, or rabbits and that the rat rod outer segments are probably devoid of the degrading activity.