Purification and properties of a new exo-(1.3)-β-D-glucanase from Bacillus circulans YK9 capable of hydrolysing resistant curdlan with formation of only laminari-biose

摘要

A (1.3)-β-D-glucan glucanohydrolase (EC 3.2.1.6), capable of hydrolysing resistant curdlan, was purified chromatographically from the culture supernatant of Bacillus circulans complex YK9 on Toyopearl HW-55F and butyl-Toyopearl 650M columns. The purified enzyme had a specific activity of 190 units mg-1 on regenerated curdlan. The molecular mass was estimated to be about 70 kDa as judged by SDS-PAGE. The enzyme had a pH optimum of approximately pH 6.0. It hydrolysed regenerated and resistant curdlans yielding predominantly laminari-biose, although the rate of hydrolysis of the former was much higher than the latter. This enzyme rapidly hydrolysed laminaran, curdlan and carboxymethyl-curdlan, but did not cleave schizophyllan and screloglucan, which have glucosyl side chains. The enzyme hydrolysed low molecular mass (1.3)-β-D-glucans (mean degree of polymerization,.DPTn = 131, 49 and 14) and laminari-heptaose more efficiently than curdlan. It also hydrolysed laminari-hexaose and -pentaose effectively, but laminari-tetraose only slightly and it did not hydrolyse laminari-triose or -biose. The enzyme is an exo-hydrolase of curdlan and various oligomers composed of (1.3)-β-D-glucosidic linkages, liberating laminari-biose from their non-reducing terminals. The laminari-biose generated was in the α-form.