STEREOCHEMICAL COURSE OF HYDROLYSIS CATALYZED BY ARABINOFURANOSYL HYDROLASES

The stereochemical course of hydrolysis catalyzed by various enzymes a cting on arabinofuranosyl linkages has been determined. H-1-NMR analys is of the action of endo-(1-->5)-alpha-L-arabinanases from Aspergillus niger and Aspergillus aculeatus showed that both hydrolyze linear ara binan with inversion of configuration, and may therefore act via a sin gle displacement mechanism. This is consistent,vith the A. niger enzym e's classification in glycosyl hydrolase family 43. The catalytic mech anisms of alpha-L-arabinofuranosidases from A. niger, A. aculeatus, As pergillus awamori, Humicola insolens, Penicillium capsulatum and Bacil lus subtilis were investigated using both H-1-NMR and high performance anion exchange chromatography to follow glycosyl transfer reactions t o methanol. In all cases these enzymes catalyzed the reaction with ret ention of configuration, and therefore probably operate via double dis placement hydrolytic mechanisms. From the results with arabinofuranosi dase A and B from A. niger we predict that all members of glycosyl hyd rolase family 51 and 54 catalyze hydrolysis with net retention of anom eric configuration. Similar studies with (1-->4)-beta-D-arabinoxylan a rabinohydrolases from A. awamori, Trichoderma reesei and Bifidobacteri um adolescentis only enabled their tentative classification as inverti ng enzymes on the basis of their lack of glycosyl transfer to methanol .