ACTION OF ACETYLXYLAN ESTERASE FROM TRICHODERMA-REESEI ON ACETYLATED METHYL GLYCOSIDES

Substrate specificity of purified acetylxylan esterase (AcXE) from Tri choderma reesei was investigated on partially and fully acetylated met hyl glycopyranosides. Methyl 2,3,4-tri-O-acetyl-beta-D-xylopyranoside was deacetylated at positions 2 and 3, yielding methyl 4-O-acetyl-beta -D-xylopyranoside in almost 90% yield. Methyl 2,3-di-O-acetyl beta-D-x ylopyranoside was deacetylated at a rate similar to the fully acetylat ed derivative. The other two diacetates (2,4- and 3,4-), which have a free hydroxyl group at either position 3 or 2, were deacetylated one o rder of magnitude more rapidly. Thus the second acetyl group is rapidl y released from position 3 or 2 after the first acetyl group is remove d from position 2 or 3. The results strongly imply that in degradation of partially acetylated beta-1,4-linked xylans, the enzyme deacetylat es monoacetylated xylopyranosyl residues more readily than di-O-acetyl ated residues, The T. reesei AcXE attacked acetylated methyl beta-D-gl ucopyranosides and beta-D-mannopyranosides in a manner similar to the xylopyranosides. (C) 1997 Federation of European Biochemical Societies .