The major portion of the hexokinase activity in brain is bound to the mitochondria. The well-known importance of lipids in the structure and function of membrane-bound enzymes prompts an investigation of the role of lipids in the interaction of brain hexokinase with the mitochondrial membrane. Specifically, we intend to examine the possibility that there may be lipid factors on both the enzyme and the membrane which are required for this interaction. Additionally, we have purified the rat brain hexokinase to homogeneity and will continue our characterization of this enzyme. Specific objectives are to determine the number of binding sites for substrates and inhibitors as well as evaluation of possible conformational alterations resulting from interaction with these compounds.