Hexokinase in astrocytes: kinetic and regulatory properties

Hexokinase (HK, EC 2.7.1.1) is a key enzyme in the control of brain glucose metabolism. The regulatory role of HK in different neural cell types has not been elucidated. In this study we determined some kinetic and regulatory properties of HK in mouse cerebrocortical astrocytes in primary culture. Astroglial HK showed an absolute requirement for Mg-ATP and D-glucose. The pH optimum of HK was between 7.4 and 8.0. For astroglial HK, the Km for Mg-ATP was approximately 208 microM and Vmax approximately 35.4 mU/mg protein. At levels higher than 0.2 mM, D-glucose-1,6-bisphosphate, a known regulator of glycolysis, inhibited astroglial HK in a concentration-dependent manner, with an IC50 of approximately 0.4 mM; at 1.2 mM, it almost completely inhibited HK activity. The results obtained for astroglial HK are compatible with those reported for the highly purified preparations of brain HK. These data are of direct relevance to the assessment of glycolytic flux and its regulation in astrocytes.