抄録
Steady-state inhibitory kinetic studies on almond β-glucosidase-catalyzed reactions were done to elucidate the binding subsite of several monosaccharides on this enzyme.
Glucono-l, 5-lactone (a transition-state analog), glucose, 2-deoxy glucose, fucose, and methyl α-glucoside showed mixed-type inhibition, but galactose, galactosamine, mannose, N-acetyl glucosamine, and glucosamine showed pure competitive inhibition on the hydrolysis of p-nitrophenyl β-glucoside.
These results are reasonably accounted for by assuming that the former monosaccharides (the mixed type inhibitors) bind to subsite 1 (the nonreducing-end side subsite to which the nonreducing-end glucose residue of a substrate binds in a productive binding mode), and that the latter (the competitive inhibitors) bind to subsite 2, the adjacent subsite to subsite 1.
The binding affinity (-ΔG°) of glucono-l, 5-lactone (-ΔG°=6.7kcalmol-1 at pH 5.0, 25°C) was significantly greater than those of the others (0.3-1.6 kcalmol-1).
