Identification of Essential Ionizable Groups of Rice α-Glucosidase II
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概要
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The essential ionizable groups of rice α-glucosidase II were identified by kinetics and chemical modification methods. The pKe of ionizable group 1 (on the acidic side) was 3.1, and that of ionizable group 2 (on the alkaline side) was 6.1. The heat of ionization of ionizable group 2, ΔH<SUB>2</SUB>, was -1.7 kcal/mol. The pH of both the pKe<SUB>1</SUB> and pKe<SUB>2</SUB> values increased by about 0.5 when the dielectric constant of the reaction medium was lowered by adding 20% methanol. The chemical modification of the active site in rice α-glucosidase II with conduritol B epoxide, an affinity labeling reagent, resulted in inactivation of the enzyme. The inactivation followed pseudo-first-order kinetics. The enzyme was protected from inactivation by a competitive inhibitor, Tris, and the partially inactivated enzymes showed only a decrease in V values and no change in K<SUB>m</SUB>. These results strongly suggest that the essential ionizable groups of rice α-glucosidase II are -C00-and -COOH.
- 日本応用糖質科学会の論文
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