β-N-Acetylglucosaminidase from Aspergillus nidulans which degrades chitin oligomers during autolysis

Abstract

A hexosaminidase from autolyzed cultures of Aspergillus nidulans was purified 196 fold and characterized as a β-N-acetylglucosaminidase (EC 3.2.1.30). The enzyme has a MW of 190 000, a pI of 4.3, and optimum pH of 5.0 and is unstable at temperatures above 50°C. The enzyme is a glyco-protein with 19.5% sugars, mannose being the principal component. It binds strongly to chitin. The enzyme hydrolyzes different substrates. The Ki with the competitive inhibitor 2-acetamido-2-deoxy-D-gluconolactone was independent of the substrate used. The enzyme was inhibited by Hg2+, Ag+, acetate and other organic anions. The kinetics of hydrolysis of chitin oligosaccharides from 2 to 6 units was studied by HPLC. This enzyme is an exoenzyme which degraded chitin oligomers gradually with the production of N-acetylglucosamine. The hydrolysis of N-N′-diacetylchito-biose was inhibited non-competitively by glucosamine and N-acetylglucosamine. In mixtures of chitin oligosaccharides, the hydrolysis of chitobiose was competitively inhibited by each of the other oligomers. © 1989.