Purification and Properties of Three Endo-xylanases from Acremonium cellulolyticus.

Abstract

Three distinct endo-xylanase components derived from Acremonium cellulase, a commercial cellulase product from a filamentous fungus Acremonium cellulolyticus, were extensively purified by consecutive column chromatographies and designated as xylanaseI, xylanase II and xylanase III. XylanasesI, IIand III were each homogeneous on both Native- and SDS-PAGE . The molecular weight (SDS-PAGE) and p1 values of xylanases I, II and III were 30 kDa and 5.1, 25 .5 kDa and 5.2, and 33.5 kDa and 5.7, respectively. The N-terminal amino acid sequences from the 1st up to the 25th residue of three enzymes were identical as follows: NH2-Ala-Glu-Ala-Ile-Asn-Tyr-Asn-Gln-Asn-Tyr-Ile-Ala-Ser-Gly-Ala-Asn-Val-Gln-Tyr-Ser-Pro-Asn-Ile-Ala-Ala-. Xylanases I, II and III had high, specific soluble xylan saccharification activities of 112.1, 86.1 and 74.8 U/mg of protein, respectively. The optimum pH and temperature for xylanases I, II and III were pH 3.5 and 55°C, pH 3.8 and 55°C, and pH 3.5 and 50°C, respectively. Xylanases I, II and III were completely stable over the ranges of pH 3.5-9.5 at 25°C for 2 h and at temperatures below 55°C, pH 3.0-9.5 and below 55°C, and pH 2.5-9.5 and below 50°C, respectively. The enzymes were almost completely inhibited by 1 mM KMnO4 and partially by 1 mM SDS, PCMB, Zn2+and Ag+ Substrate specificities and kinetic parameters for these enzymes were precisely examined. The enzymes were characterized as endo-type xylanases on the basis of their action patterns on soluble xylan and xylooligosaccharides. Xylanases I, II and III seem to be isoforms judging from N-terminal amino acid sequences and basic physicochemical and enzymatic properties as well as substrate specificities.