Interaction of hexokinase with the outer mitochondrial membrane and a hydrophobic matrix

The major portion of rat brain hexokinase (HK type I) is bound to the outer membrane of mitochondria and glucose-6-phosphate (G6P) can release the bound enzyme. In an attempt to look at the 'hydrophobic' component of binding, interaction of the enzyme with a purely hydrophobic matrix, palmityl-substituted Sepharose-4B (Sepharose-lipid) was investigated. Hexokinase readily bound to this matrix with retention of its catalytic activity. Glucose-6-phosphate which has a releasing effect on the mitochondrially bound enzyme, enhanced binding of the enzyme on the hydrophobic matrix. Chymotrypsin treatment of hexokinase which causes loss of binding to mitochondria, also results in loss of adsorption to the hydrophobic matrix, thus demonstrating that the 'hydrophobic tail' present at its N-terminal end is essential for binding in both cases. Data presented provide some new information relevant to understanding how hexokinase interacts with its natural binding matrix, the mitochondrion.