Reactive thioglucoside substrates for ß-glucosidase.
Arch Biochem Biophys
; 537(1): 1-4, 2013 Sep 01.
Article
em En
| MEDLINE
| ID: mdl-23811198
ABSTRACT
A new, very efficient, class of thioglycoside substrates has been found for ß-glucosidase. While thioglycosides are usually resistant to hydrolysis, even in the presence of acids or most glycohydrolases, the ß-D-glucopyranosides of 2-mercaptobenzimidazole (GlcSBiz) and 2-mercaptobenzoxazole (GlcSBox) have been found to be excellent substrates for ß-glucosidase from both sweet almond (a family 1 glycohydrolase) and Aspergillus niger (a family 3 glycohydrolase), reacting nearly as well as p-nitrophenyl ß-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 kcat/KM does not show a detectable solvent deuterium kinetic isotope effect (SKIE), but unlike the hydrolysis of phenyl thioglucosides, a modest SKIE is seen on kcat [(D2O)kcat=1.28 (±0.06)] at the pL optimum (5.5≤pL≤6.6). A solvent isotope effect is also seen on the KM for the N-methyl analog of GlcSBiz. These results suggest that the mechanism for the hydrolysis of the ß-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.
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01-internacional
Base de dados:
MEDLINE
Assunto principal:
Tioglucosídeos
/
Beta-Glucosidase
Idioma:
En
Ano de publicação:
2013
Tipo de documento:
Article