Ketohexokinase, isoenzymes of glucokinase and glycogen synthesis from hexoses in neonatal rat liver

Abstract

The incorporation of [14C] fructose into glycogen in rat-liver slices indicates the neonatal development of a pathway for the conversion of this hexose into glycogen. The activity of ketohexokinase increases 15-fold from the 18-day foetus to the adult. The rates of incorporation of [14C]galactose into liver glycogen in slices indicate that this system has most activity during the period of milk feeding. The activity of hepatic glucokinase in the adult rat is eight times the value 15 days after birth and four times the value in the 17-day foetus. The incorporation of [14C]glucose into glycogen is also greater in slices from adult and foetal liver than from 15-day liver. There are two iso-enzymes of glucokinase in rat liver. The only form in the foetus has a maximum activity at pH 9.0 and Km for glucose 5-8 x 10-5 M. This isoenzyme comprises 15% of the liver-glucokinase activity in the adult. An isoenzyme with Km for glucose 1-3 x 10-2 M is the major component in the adult. An extract of adult liver has maximal activity for glucokinase at pH 7[center dot]0. These findings have been discussed with reference to the changing pattern of carbohydrate metabolism during neonatal development of liver in the rat.