Properties of the glucose 6-phosphate-solubilized brain hexokinase: Evidence for a lipoprotein complex

Abstract

1. 1. Glucose 6-phosphate ( Glc-6-P )-solubilized brain hexokinase is part of a large aggregate as shown by its appearance in the void volume upon Sephadex G-200 and Sepharose 4B column chromatography. 2. 2. Thin-layer chromatography of chloroform-methanol (2:1, v/v) extracts indicate the presence of cholesterol, phosphatidylethanolamine and, tentatively, one or more neutral lipid components in the Glc-6-P supernatant but not in a control supernatant prepared by incubation in the absence of Glc-6-P and lacking significant hexokinase activity. 3. 3. The Glc-6-P supernatant has a phosphorus to protein ratio of 9 ± 2 μ g P/mg protein which is in rough agreement with the values reported, in the literature for brain mitochondrial membranes. 4. 4. Mitochondria, rendered lipid deficient by treatment with cold 10 % aqueous acetone, lost 80–95 % of their total hexokinase activity and this activity could be partially restored by incubation with phosphatidylethanolamine but not with phosphatidylcholine nor phosphatidylserine. Complete recovery of activity was obtained in preparations which had lost no more than 60 % of their activity. 5. 5. Digitonin prevents the MgCl 2-mediated rebinding of hexokinase to the mitochondrial membrane at concentrations which do not solubilize hexokinase from intact mitochondria.