Reactive thioglucoside substrates for ¦Â-glucosidase

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• 作者：Elizabeth Alverson-Banks Avegno ; Scott J. Hasty ; Archana R. Parameswar ; Gary S. Howarth ; Alexei V. Demchenko ; Larry D. Byers
• 关键词：¦Â-Glucosidase ; 2-Mercaptobenzimidazoyl ¦Â-thioglucopyranoside ; Solvent kinetic isotope effect ; Retention
• 刊名：Archives of Biochemistry and Biophysics
• 出版年：2013
• 出版时间：1 September, 2013
• 年：2013
• 卷：537
• 期：1
• 页码：1-4
• 全文大小：502 K

文摘

A new, very efficient, class of thioglycoside substrates has been found for ¦Â-glucosidase. While thioglycosides are usually resistant to hydrolysis, even in the presence of acids or most glycohydrolases, the ¦Â-d-glucopyranosides of 2-mercaptobenzimidazole (GlcSBiz) and 2-mercaptobenzoxazole (GlcSBox) have been found to be excellent substrates for ¦Â-glucosidase from both sweet almond (a family 1 glycohydrolase) and Aspergillus niger (a family 3 glycohydrolase), reacting nearly as well as p-nitrophenyl ¦Â-d-glucoside. The enzyme-catalyzed hydrolysis of GlcSBiz proceeds with retention of configuration. As with the (1000-fold slower) hydrolysis of phenyl thioglucosides catalyzed by the almond enzyme, the pL (pH/pD)-independent k_cat/K_M does not show a detectable solvent deuterium kinetic isotope effect (SKIE), but unlike the hydrolysis of phenyl thioglucosides, a modest SKIE is seen on k_cat [^D₂Ok_cat = 1.28 (¡À0.06)] at the pL optimum (5.5 ? pL ? 6.6). A solvent isotope effect is also seen on the K_M for the N-methyl analog of GlcSBiz. These results suggest that the mechanism for the hydrolysis of the ¦Â-thioglucoside of 2-mercaptobenzimidazole and of 2-mercaptobenzoxazole involves remote site protonation (at the ring nitrogen) followed by cleavage of the thioglucosidic bond resulting in the thione product.