A β-N-acetylhexosaminidase from Penicillium oxalicum implicated in its cell-wall degradation

High β‐N‐acetylhexosaminidase (EC.3.2.1.52) activity was detected during autolysis of Penicillium oxalicum. Purification of the enzyme to homogeneity yielded an enzyme with a molecular weight of 132 000 Da by gel filtration and 71 900 Da by SDS polyacrylamide gel electrophoresis, suggesting a dimeric structure. The enzyme is an acidic protein with a pl of 5.0. Optimal activity was at pH 4.0 and 40°C, with a Km of 0.80 mmol 1‐1 for p‐nitrophenyl‐β‐N‐acetylglucosaminide and 1.03 mmol 1‐1 for p‐nitrophenyl‐β‐N‐acetylgalactosaminide. The Ki with the competitive inhibitor O‐(2‐acetamido‐2‐deoxy‐D‐glucopyranosylidene) amino‐N‐phenylcarbamate was 1 μmol 1‐1. Hg2+, Ag+ and Fe3+ were effective inhibitors. β‐N‐acetylhexosaminidase hydrolysed chitobiose, chitotriose, chitotetrose and chitopentose to monomer to an extent of 92, 74, 44 and 17% respectively in 40 min. This enzyme, in conjunction with a purified endochitinase from P. oxalicum, hydrolysed a cell‐wall chitin fraction isolated from this fungus, with the production of N‐acetylglucosamine.