THE MECHANISM OF INSULIN-INDUCED INCREASE OF THE RATE OF DE NOVO PURINE BIOSYNTHESIS IN PRIMARY CULTURED RAT HEPATOCYTES: 212

Abstract

The de novo purine biosynthesis was studied 8 hours after the administration of insulin. The rate of de novo purine biosynthesis assayed by [14C]formate incorporation started to increase at the insulin concentration of 10−10M and reached the plateau at 10−7M or above with its level 2.8 folds higher than control. 5-phosphoribosyl 1-pyrophosphate(PRPP) availability assayed by [14C]adenine incorporation increased steeply and reached the plateau with its level 2.3 folds higher than control at 10−9M and stayed at this level in the higher concentration. By the addition of Actinomycin D(lμg/ml) or cycloheximide(lμg/ml) increased rate of de novo purine biosynthesis and increased PRPP availability decreased to the control level. Amidophosphoribosyltransferase(ATase) activity per unit amount of protein or DNA increased 1.5 to 1.8 folds with increased Vmax and unchanged Km for PRPP. ATP concentration increased by 27% which was counterbalanced with decreased concentrations of AMP(73%), ADP(69%), GMP(73%) and GDP(79%) concentration. Results of these studies suggest that insulin increases the rate of de novo purine biosynthesis by increasing ATase activity and PRPP availability.