Study of hexokinase binding site on mitochondrial outer membrane in brain tumor cells

In brain tumors, the main source of energy is from glycolysis, which is initiated by hexokinase type I (HK-I), an enzyme bound to the outer mitochondrial membrane, involving two sets of binding sites. In addition to the glucose-6-phosphate (G6P)-sensitive site (Type A), the enzyme is bound on a second set of sites (Type B) which are insensitive to G6P, but totally releasable by high concentrations of chaotropic salts such as KSCN. In the present study, we investigate possible changes in HK-I binding to the outer mitochondrial membrane during malignancy. In this experimental study, 2 mM G6P was used for releasing enzyme from site A, while site B was depleted using a mixture of KSCN and KCl with a total concentration of 45 mM. For blocking binding sites in site A, dicyclohexylcarbodiimide (DCCD) was used. DCCD, which normally has the capacity to block HK-I binding at site A, was found ineffective for mitochondria obtained from astrocytoma and glioma specimens, presumably due to changes in the microenvironment of Glu 72 of porin with which it interacts. It also appears that increased incorporation of cholesterol, reported to occur in the mitochondria of cancer cells, may influence HK binding due to changes in mitochondrial membrane fluidity. Taken together, these results support earlier conclusions on possible changes in the microenvironment of bound HK-I and also fluidity of membrane upon malignancy.