title: Steric course of the hydration of D-gluco-octenitol catalyzed by alpha-glucosidases and by trehalase.
abstract: Crystalline Aspergillus niger alpha-glucosidase and highly purified preparations of rice alpha-glucosidase II and Trichoderma reesei trehalase were found to catalyze the hydration of [2-(2)H]-D-gluco-octenitol, i.e., (Z)-3,7-anhydro-1,2-dideoxy-[2-2H]-D-gluco-oct-2-enitol, to yield 1,2-dideoxy-[2-2H]-D-gluco-octulose. In each case, the stereochemistry of the reaction was elucidated by examining the newly formed centers of asymmetry at C-2 and C-3 of the hydration product. The C-1 to C-3 fragment of each isolated [2-2H]-D-gluco-octulose product was recovered as [2-2H]propionic acid and identified by its positive optical rotatory dispersion as the S isomer, showing that each enzyme had protonated the octenitol (at C-2) from above its re face. 1H NMR spectra of enzyme/D-gluco-octenitol digests in D2O showed that the alpha-anomer of [2-2H]-D-gluco-octulose was exclusively produced by each alpha-glucosidase, whereas the beta-anomer was formed by action of the trehalase. The trans hydration catalyzed by the alpha-glucosidases was found to be very strongly inhibited by the substrate; the cis hydration reaction catalyzed by the trehalase showed no such inhibition. Special importance is attached to the finding that in hydrating octenitol each enzyme creates a product of the same anomeric form as in hydrolyzing an alpha-D-glucosidic substrate. This result adds substantially to the growing evidence that individual glycosylases create the configuration of their reaction products by a means that is independent of donor substrate configuration, that is, by a means other than "retaining" or "inverting" substrate configuration.
authors.affiliation: Chemisches Laboratorium, Universität Freiburg, West Germany.
authors.forename: W
authors.initials: W
authors.lastname: Weiser
authors.forename: J
authors.initials: J
authors.lastname: Lehmann
authors.forename: S
authors.initials: S
authors.lastname: Chiba
authors.forename: H
authors.initials: H
authors.lastname: Matsui
authors.forename: C F
authors.initials: CF
authors.lastname: Brewer
authors.forename: E J
authors.initials: EJ
authors.lastname: Hehre
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology; D003903:Deuterium; D007700:Kinetics; D012275:Oryza / Q000201:enzymology; D012639:Seeds / Q000201:enzymology; D013402:Sugar Alcohols / Q000378:metabolism*; D014198:Trehalase / Q000378:metabolism*; D014242:Trichoderma / Q000201:enzymology; D000520:alpha-Glucosidases / Q000378:metabolism*
chemical_list: D013402:Sugar Alcohols; C056279:3,7-anhydro-1,2-dideoxygluco-oct-2-enitol; D003903:Deuterium; D000520:alpha-Glucosidases; D014198:Trehalase