Evaluation of catalytic activity and synergism between two xylanase isoenzymes in enzymic hydrolysis of two separate xylans in different states of solubility

Abstract

Synergism of two xylanase (1,4) β- d-xylan xylanohydrolase, EC 3.2.1.8) isoenzymes from Streptomyces A451 was observed in enzymic hydrolysis of water-soluble and -insoluble fractions of two commercial xylan preparations. The reaction modes were determined qualitatively by TLC and quantitatively by GLC. With oat-spelt xylan as substrate, the total amount of xylose and xylobiose produced by using xylanase I and xylanase II in sequence was significantly higher than that by xylanase I or xylanase II individually, while the amounts of the relatively higher-molecular-weight oligosaccharides xylotriose to xylopentaose obtained by using isoxylanases individually were more than those obtained by using isoxylanases in sequence. A time-course study on the release of hydrolysis products over a 24-h period revealed that higher oligosaccharides were released initially followed by release of simpler sugars. A study of the hydrolysis of model oligosaccharides by crude enzyme preparation revealed a preference for higher oligosaccharides and demonstrated that xylopentaose was hydrolyzed to xylose, xylobiose, and xylotriose. A comparison was made of the hydrolysis of two different xylans, birchwood (hardwood) and oat-spelt (softwood), by crude xylanase. Product profiles showed that there were significant differences between the range and amounts of products released from the two different xylans. Studies on relative specific activities showed that xylanase II had overall lower specific activity toward various xylans than did xylanase I, and xylanase I, xylanase II, and crude xylanase showed lower specific activity toward insoluble xylan fractions than toward soluble xylan fractions. In addition, the reduction in specific activity was greater for insoluble birchwood than for insoluble oat-spelt xylan.