|Cote, Gregory - Greg|
Submitted to: Carbohydrate International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/1998
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The substrate specificities of acetylxylanesterases (AcXEs) from Schizophyllum commune, Trichoderma reesei, and Streptomyces lividans, were compared with those of wheat germ lipase, orange peel esterase, and Candida cylindracea lipase. Aryl acyls, acetylated methyl glycosides, and acetylxylan were used as substrates. The last three enzymes were unable to deacetylate xylan or deacetylate it to a degree leading to its precipitation from a solution. AcXE from Streptomyces lividans was the only enzyme which did not attack aryl acyls. Relative activities of other tested enzymes, with exception of C. cylindracea lipase, decreased in the order 4-nitrophenyl acetate, propionate, and butyrate. In methyl 2,3,4-tri-O-acetyl beta-D-xylopyranoside and methyl 2,3,4,6- tetra-O-acetyl beta-D-glucopyranoside AcXEs showed preference for deacetylation of positions 2 and 3. This regiospecificity corresponded to the function of AcXEs in acetylxylan degradation and was found to be complementary to that exhibited by non-hemicellulolytic enzymes, thus offering new perspectives in synthetic carbohydrate chemistry. AcXEs seem to utilize a different mechanism of deacetylation than other esterases. Based on kinetics of deacetylation of diacetates of methyl beta-D-xylopyranoside, it has been hypothetized that the mechanism of deacetylation of the positions 2 and 3 when the neighboring positions 3 and 2 are non-acetylated, by AcXEs, might involve an enzyme-catalyzed formation of a five-membered transition state from which acetyl group is released.