Structural effect of amine N-oxides on the facilitation of α-glucosidase-catalyzed hydrolysis reactions

Activation and stabilization of enzymes is an important issue in their industrial application. We recently reported that synthetic betaines, derived from cellular metabolites, structure-dependently increased the activity and stability of various enzymes including hydrolases, oxidases, and synthetases simply by mixing them into the reaction buffer. In this report, we focus on amine N-oxides, which are similarly important metabolites in cells with a highly polarized N-oxide bond, and investigate their enzyme stabilization and activation behavior. It was revealed that synthetic amine N-oxides structure-dependently activate α-glucosidase-catalyzed hydrolysis reactions similarly to betaines. The subsequent comparison of the kinetic parameters, the optimal concentration range for activation, and the maximal activity, suggested that amine N-oxides facilitate hydrolysis reactions via the same mechanism as betaines, because no differences were confirmed. However, the enzyme stabilization effect of amine N-oxides was slightly superior to that of betaines and the temporal stability of the enzyme in aqueous solutions was higher in the low amine N-oxide concentration range. The rheological properties, CD spectra, and dynamic fluorescence quenching experiments suggested that the suppression of unfavorable conformational perturbation was related to the difference in the hydration environments provided by the surrounding water molecules. Thus, we clarified that amine N-oxides facilitate enzyme reactions as a result of their similarity to betaines and provide a superior stabilizing effect for enzymes. Amine N-oxides show potential for application in enzyme storage and long-term reactions.

Increased yield of β-glucosidase-catalyzed hydrolysis reactions in the presence of betaine-type metabolite analog

β-Glucosidases (EC 3.2.1.21), abundant enzymes distributed in animals, plants and microorganism, has been generating lots of attentions for bioethanol production from cellulosic biomass. In this study, using three different origins of β-glucosidases, glucose productivity of β-glucosidase-catalyzed hydrolysis reactions in the presence of synthetic betaine-type metabolite analog (2-N,N,N-tri-n-butylammonium) acetate, was investigated. By the addition of the analog, the hydrolysis yields for all β-glucosidases was highly improved from 4-13 to 64-100 %. To understand the factors affecting on the yield enhancements, the kinetic parameters, inhibition constants of end-product and temporal stability of β-glucosidases were compared. As a result, enhancement of the yields is mainly related to the increase in the temporal stability of β-glucosidases in the presence of the analog. The present findings lead to not only improve the glucose productivity of β-glucosidase-catalyzed hydrolysis reaction toward bioethanol production but also apply to a new stabilization method for various unstable enzymes.