In most tissues, the phosphorylation of glucose is catalyzed by hexokinase , one of three regulatory enzymes of glycolysis (see also phosphofructokinase and pyruvate kinase ). Hexokinase has broad substrate specificity and is able to phos- phorylate several hexoses in addition to glucose. Hexokinase is inhibited by the reaction product, glucose 6-phosphate, which accumulates when further metabolism of this hexose phosphate is reduced. Hexokinase has a low K m (and, therefore, a high affin- ity, see p. 59) for glucose. This permits the efficient phosphoryla- tion and subsequent metabolism of glucose even when tissue concentrations of glucose are low (Figure 8.13). Hexokinase , however, has a low V max for glucose and, therefore, cannot sequester (trap) cellular phosphate in the form of phosphorylated hexoses, or phosphorylate more sugars than the cell can use.