Yeast hexokinase in solution exhibits a large conformational change upon binding glucose or glucose 6-phosphate

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Abstract
Using small-angle X-ray scattering from solutions of yeast hexokinase, the radii of gyration of the monomeric B isozyme and its complexes with sugar substrates was measured. The radius of gyration decreases by 0.95 .+-. 0.24 .ANG. on binding glucose and 1.25 .+-. 0.28 .ANG. on binding G-6-P. This observed reduction in radius of gyration in the presence of glucose is the same as that calculated from the coordinates of the high-resolution crystal structures of native hexokinase B and a glucose complex with hexokinase A. These measurements suggest that the dramatic closing of the slit between the 2 lobes of hexokinase observed in the crystal structures occurs in solution when either glucose or G-6-P is bound.