A BETA-N-ACETYLHEXOSAMINIDASE FROM PENICILLIUM-OXALICUM IMPLICATED IN ITS CELL-WALL DEGRADATION

High beta-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 pi of 5.0. Optimal activity was at pH 4.0 and 40 degrees C, with a K-m of 0.80 mmol 1(-1) for p-nitrophenyl-beta-N-acetylglucosaminide and 1.03 mmol 1(-1) for p-nitrophenyl-beta-N-acetylgalactosaminide. The K-i with the competitive inhibitor O-(2-acetamido-2-deoxy-D-glucopyranosylidene) amino N-phenylcarbamate was 1 mu mol 1(-1). Hg2+, Ag+ and Fe3+ were effective inhibitors. beta-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.