A mitochondrial-binding hexokinase found in brain and in hepatomas is believed to be very important in regulation of energy metabolism. This enzyme is 100 kDa with two 50 kDa, highly homologous halves. The N- terminal half is believed to contain a glucose-binding site important in product inhibition and binding to the mitochondrial outer membrane. Mutagenesis of specific amino acids in the N-terminal half fail to affect activity a product inhibition. Further studies are needed on this hexokinase to define the sites involved in production inhibition and mitochondrial binding. Since this hexokinase plays a major role in neuronal energy metabolism, defining its regulation is of fundamental importance to understanding aberrations in energy metabolism that may underlay age-associated diseases.