Hexokinases catalyze the reaction of cytosolic alpha-D-glucose and ATP to form alpha-D-glucose 6-phosphate and ADP. Nine rice isozymes capable of acting on cytosolic glucose have been identified in complementation studies with hexokinase-deficient mutant yeast strains. One of these, HXK7, has been localized to the cytosol; the localization of the others has not been experimentally established. The nine isozymes differ in the patterns of expression in various plant tissues and in the course of plant development, consistent with the hypothesis that expression of hexokinase plays a role in the differential regulation of glycolysis in specialized tissues (Cho et al. 2006).