Changes in the kinetic parameters of hepatic gamma-glutamyltransferase from streptozotocin-induced diabetic rats

Previous research has shown that the enzymatic activity of hepatic gamma -g lutamyltransferase was increased in streptozotocin-induced diabetic rats wi th no increase in the expression of the protein. The current work has chara cterized the differences in the kinetic properties of hepatic gamma -glutam yltransferase from diabetic versus control rats. Hepatic gamma -glutamyltra nsferase was purified from control male and female rats and from rats made diabetic 30 days previously with streptozotocin. The maximal velocity and t he Michaelis constant were determined for the purified enzyme with two sepa rate donors (L-gamma -glutamyl-p-nitroanilide or L-gamma -glutamyl-(7-amido -4-methylcoumarin)) in the presence of one of eight accepters ((L)-alanine- glycine, L-glycine-glycine, L-methionine, L-glutamate, L-alanine, L-glutami ne, L-phenylalanine or (L)-aspartate). With both donors, hepatic gamma -glu tamyltransferase from diabetic rats had a consistently higher kinetic effic iency than gamma -glutamyltransferase from controls. The kinetic efficiency percent increase of diabetic over control gamma -glutamyltransferase when averaged across all accepters was higher in males than in females. With (L) -gamma -glutamyl-p-nitroanilide, the kinetic efficiency increase of diabeti c over control gamma -glutamyltransferase was higher with poor accepters th an with highly efficient accepters. These data indicate that there are diff erences in the physical properties of hepatic gamma -glutamyltransferase fr om diabetic versus control rats and from female versus male rats. (C) 2001 Elsevier Science B.V. All rights reserved.