Release of Brain Mitochondrial Hexokinase by Acidic Proteins and Macromolecular Polyanions
Preparations of arachidonic acid binding and non-binding proteins from bovine brain, four acidic proteins (alpha-casein, phosvitin, beta-lactoglobulin A and B), the peptide polyglutamate, and two polyanions (heparin, dextran sulfate) enhanced both basal and glucose 6-phosphate induced solubilization of rat brain mitochondrial hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1). In contrast, three other acidic proteins, had little (alpha-lactalbumin) or no effect (bovine serum albumin, ovalbumin) and five basic proteins inhibited release of the enzyme. Solubilizing activity therefore appears to require a net negative charge and one or more of the following structural features: extended conformation, random coil, and unordered or beta-structure, in the latter case, as the beta-barrel in the fatty acid binding proteins and beta-lactoglobulins. It is of interest that a difference of a single negative charge between beta-lactoglobulin A and B, resulted in a statistically significant difference in the stimulation of hexokinase release. Possible physiological and pathological roles of this hexokinase solubilizing effect are discussed briefly.