Table III.

Maize root HXK kinetic parameters for the phosphorylation of hexoses

	Glca	Man	3-OMGa	ATP
Km (μmol L−1)	76 ± 9	105 ± 40	21,000 ± 7,000	42 ± 8
Vmax (μmol min−1 mg protein−1)	2.52 ± 0.31	1.26 ± 0.06	0.007 ± 0.002	2.16 ± 0.32
103 × Vmax/Km(min−1 mg protein−1 L)	33	12	3.10−4	51

The K_m and V_max values were calculated using the Lineweaver-Burk reciprocal plot method. Data are the mean of three measurements from two independent HXK preparations.

^aHXK activity was inhibited to the same extent with either Glc (2 mm) or 3-OMG (50 mm), when measured in the presence of either 10 mm ZnCl₂ (55% inhibition) or 0.5 mm ADP (15% inhibition). With 10 mm mannoheptulose, Glc and 3-OMG phosphorylations were inhibited by 31% and 78%, respectively.