甜杏仁之葡萄甘酵素的特性與抑制作用之研究

Abstract

本實驗以Protein-PakQ分離得另一罕見之同功酵素,其為單分子性的醣蛋 白,分子量39,000,pI=4.55.我們設計並合成出ㄧ系列咪唑類化合物,研究 發現這一咪唑化合物均是beta-葡萄糖甘酵素極強的可逆抑制劑,其中 以4-(3'-苯丙基)咪唑為最佳,其Ki值為0.073毫莫耳體積濃度.由結果 示 醣基結合副位與非醣基結合副位間之最適化距離為三個次甲基.又由pH- dependence實驗顯示,去質子化的抑制劑與單一質化酵素之結合能是真正 抑制作用酵素與抑制劑之結合型態.而4-(3'-苯丙基)咪唑與如此強之結合 關係可以比擬為受質在過渡狀態時與酵素的結合情形.Here,we report that a new isozyme of beta-glucosidase wasrified from the commerically available crude product of sweet almond protein and found to be a monomeric glycoprotein with Mr.39,000, pI=4.55. A series of imidazole derivaties were designed and synthesized.Resoults showed that this group of imidazoles are very potent inhibitors of beta-glucosidase with the lowest Ki value of 7.3*10-8 M.This reveals that the two binding subsites are distant with the optimal distance around 3 methylene groups. The pH-dependence indicates that most likely the unprotonated inhibitor binds most tightly to the catalytically active species of the enzyme. The tightly bindingld might be explained by the mimic structure of substratehe transition state.