Environmental effects on glutathione-insulin transhydrogenase in rat liver.

The dietary and hormonal regulation of the level of glutathione-insulin tranhydrogenase in rat liver was investigated in these studies. In order to make valid comparisons, the assay of glutathione-insulin transhydrogenase was performed at near zero-order kinetics wherein enzyme rate was proportional to enzyme amount. Changing the protein content of the diet or administration of glucagon or cortisone did not significantly affect the specific activity of glutathione-insulin transhydrogenase in microsomes from rat liver. However, the Vmax and Km of this enzyme in the livers of adrenalectomized rats were increased three-and fourfold over these values in microsomes from normal liver. Administration of cortisone resulted in a return to the normal kinetic constants of microsomal GIT within 4 hr.