Mitochondrial Hexokinase

Abstract

The particulate hexokinase of ascites tumor, Sarcoma 37, is shown to be mitochondrial.The activity is readily solubilized by glucose 6-phosphate, ribonucleoside triphosphates, or high salt concentration with differing pH dependencies.Specificity and kinetic studies suggest that the effect of glucose-6-P is related to the regulator site on the enzyme.The enzyme can be bound again to previously eluted mitochondria in a Mg++-dependent equilibrium (and, more weakly, in the absence of added metal ions).The interaction follows a simple over-all equation, (binding sites) + (enzyme) + Ok++) G (complex), represented by a single equilibrium constant.Mitochondria from tumor, liver, and brain have binding sites.Soluble enzyme from tumor, brain, and skeletal muscle can be bound to a large extent to tumor mitochondria.Soluble liver hexokinase and eluted tumor hexokinase which has been incubated with liver extract are not bound.Loss of ability to bind is attributed to a lysosomal cathepsin, and is also brought about by very small amounts of chymotrypsin.The tumor mitochondrial hexokinase is not in the compartment of oxidative phosphorylation, as shown by kinetic competition studies for oxidatively generated adenosine triphosphate and the lack of effect of atractyloside on the action of hexokinase on added ATP. 1 I.