Enzymes of glucose metabolism in cultured human gliomas: neoplasia is accompanied by altered hexokinase, phosphofructokinase, and glucose-6-phosphate dehydrogenase levels.

The enzymes of glycolysis and selected enzymes of the pentose phosphate pathways were measured by fluorometric methods in extracts prepared from cultures of normal cortical human astrocytes and from cultures derived from low-grade (II) or high-grade (IV) gliomas. The hexokinase and phosphofructokinase levels of the low-grade glioma-derived line were not significantly different from those of the normal astrocyte cultures. However, the activities of hexokinase and phosphofructokinase were consistently and significantly increased in the high-grade glioma-derived lines. The activity of glucose-6-phosphate dehydrogenase was significantly decreased in all glioma-derived lines and by more than 90% in the high-grade-derived lines. Other enzymes of the glycolytic pathway were not significantly different from those of normal astrocytes, or they showed a variation inconsistently related to the neoplastic state. Glucose flux is not apparently regulated to a significant degree of hexokinase in glioma-derived lines, since the measured Vmax values are in substantial excess over the measured flux rates. Reversible binding of hexokinase to the particulate fraction was observed in both the normal astrocytes cultures and the high-grade glioma-derived lines. A twofold displacement of particulate hexokinase by ATP, ADP, 1-O-methylglucose, sorbitol-6-phosphate, and dibutyryl cyclic AMP was observed in the high-grade glioma-derived lines. The degree of displacement by various agents and the basal ratio of free/bound was not significantly different between the transformers and the nontransformants. The hexokinase from both the gliomas and the normal astrocytes was noncompetitively inhibited by the glucose analogue 2-deoxy-d-glucose. Phosphofructokinase activity is close to the observed glucose flux rates in both the normal astrocyte and the glioma-derived cultures. The phosphofructokinase activity of normal astrocytes is activated twofold or more by ADP, AMP, fructose-2,6-diphosphate, and Pi. However, these same ligands activate phosphofructokinase by less than twofold in a typical high-grade glioma-derived line. ATP, dibutyryl cyclic AMP, and citrate inhibit glioma and normal astrocytic phosphofructokinase, but the magnitude of the inhibition is much less than in the glioma-derived lines.