Abstract :
[en] The recombinant b-O-glucosidase (EC 3.2.1.21) from the thermophilic bacterium Tp8 does not
catalyse glucosinolate degradation but transforms desulfo-glucosinolates viz. desulfo-sinigrin,
desulfo-gluconapin, desulfo-progoitrin, desulfo-epiprogoitrin, desulfo-glucotropaeolin, desulfogluconasturtiin, desulfo-sinalbin, desulfo-limnantin, desulfo-glucoerucin and desulfo-glucoiberin in the corresponding pure nitriles (GC purity: +/- 99%). Prop-3-enyl, but-3-enyl, (2R)-2-hydroxybut-3-enyl, (2S)-2-hydroxybut-3-enyl, benzyl, phenethyl, 4-hydroxybenzyl, 3-methoxybenzyl, 4-methylthiobutyl and 3-methylsulphinylpropyl cyanides have been respectively identified by GC-MS. This thermostable enzyme is very different from myrosinase, a b-S-glucosidase (EC 3.2.3.1) present in Brassicaceae, which easily hydrolyses glucosinolates producing mainly a mixture of isothiocyanates, nitriles and eventually thiones. This endogenous b-S-glucosidase is totally inactive towards desulfo-glucosinolates, while the b-O-glucosidase tested is not active with synthetic S-glucose substrates such as the p-nitrophenyl-S-glucose. It is the first time that a b-O-glucosidase has been found to hydrolyse natural S-glucose substrates such as desulfoglucosinolates.
The possibility to produce pure nitriles by this way, especially chiral compounds
((2R)-2-hydroxybut-3-enyl, (2S)-2-hydroxybut-3-enyl...), appears to be interesting for application in fine chemistry. The effect of pH (2 to 9) and temperature (40 to 85°C) on the recombinant b-O-glucosidase activity has been determined with desulfo-sinigrin as substrate. Optimal activity of this thermostable enzyme is reached at pH 6.
