好アルカリ性バチルス属細菌が生産する耐熱性アルカリキシラーゼ

Abstract

Land plants are mainly composed of cellulose, hemicellulose and lignin. Xylans are major components of hemicellulosic polysaccharides, and one of the most abundant biopolymers. The main chain of xylans from all land plants is based on a β-1, 4-D-xylopyranosyl linkage. This main chain is substituted with a variable number of neutral or uronic monosaccharide, short oligosaccharide side chains, or non-saccharide substituents. Most of xylans are consequently heteropolysaccharides containing L-arabinofuranose, D-galactopyranose and D-glucuronopyranose. Lignin is one of the non-saccharide substituents. Structure of xylans varies in the nature and degree of branching of the main chain.So-called xylanases hydrolyze the β-1, 4-linked xylopyranosyl main chain of land plant xylans to produce xylose or xylooligosaccharides. Xylanases can hydrolyze not only soluble xylans but also insoluble ones bound to cellulose. Therefore, xylanases can break down xylans remaining in pulp. A part of lignin can be consequently removed from the pulp by treatment with xylanases. This “bio-bleaching” process would possibly decrease the amount of chlorine used for pulp bleaching. Toxic or carcinogenic chlorinated compounds have been produced from wood components with the chlorine and thrown into environments.Xylanases have been isolated from various bacteria and fungi. Most of microbial xylanases show the enzymic activities at acidic or neutral pH regions. We have investigated alkaliphilic microorganisms, that are one of extremophiles, and their enzymes.Several xylanases have been isolated from alkaliphiles during a course of the investigation. Some of them are alkaline-active and thermostable. These alkaline xylanases might be suitable for the bio-bleaching process, because the pulp is generally processed at a high alkaline pH and high temperature condition. This article reviews the β-1, 4-xylanases produced by alkaliphiles that have been isolated.