Sigmoidal kinetics of glucokinase.

Glucokinases obtained from the liver of several species of mammals and amphibians exhibit sigmoidal saturation functions for glucose. Hill coefficients (nH) are about 1.5, and half-saturation values (K0.5) lie between 1.5 and 8.5 mmol/l. The nH and K0.5 values are constant throughout the purification steps of rat glucokinase. A dimeric form of rat glucokinase appearing in aged preparations exhibits michaelian kinetics. Sigmoidal kinetics is considered as an adaptive feature of glucokinases to increase the efficiency of the liver uptake of glucose at the changeable concentrations in the blood resulting from variations in the amount of dietary glucose.