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.