The Company of Biologists

Table 1.

Kinetic and regulatory parameters of isozymes of mammalian hexokinase^{^a}

	K_m (mmol 1^-1)
Isozyme	for Glc	for ATP	K_i (mmol 1^-1) for Glc-6-P	Effect of P_i
Type I	0.03	0.5	0.02	Low concentrations antagonize inhibition by Glc-6-P; high concentrations inhibit
Type II	0.3	0.7	0.02	Inhibitory at all concentrations
Type III	0.003^{^b}	1.0	0.1	Inhibitory at all concentrations
Glc, glucose; Glc-6-P, glucose-6-phosphatase.

	K_m (mmol 1^-1)
Isozyme	for Glc	for ATP	K_i (mmol 1^-1) for Glc-6-P	Effect of P_i
Type I	0.03	0.5	0.02	Low concentrations antagonize inhibition by Glc-6-P; high concentrations inhibit
Type II	0.3	0.7	0.02	Inhibitory at all concentrations
Type III	0.003^{^b}	1.0	0.1	Inhibitory at all concentrations
Glc, glucose; Glc-6-P, glucose-6-phosphatase.

A range of values have been reported by various investigators (for a compilation, see Wilson,1985); the values shown here are representative.

Substrate inhibition is seen at higher Glc concentrations (approx. 1 mmol 1^-1).