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 n ot been elucidated. In this study we determined some kinetic and regulatory properties of HK in mouse cerebrocortical astrocytes in primary culture. A stroglial HK showed an absolute requirement for Mg-ATP and D-glucose. The p H optimum of HK was between 7.4 and 8.0. For astroglial HK, the K-m for Mg- ATP was similar to 208 mu M and V-max similar to 35.4 mU/mg protein. At lev els higher than 0.2 mM, D-glucose-1,6-bisphosphate, a known regulator of gl ycolysis, inhibited astroglial HK in a concentration-dependent manner, with an IC50 of similar to 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.