抄録
Exo-maltohexaohydrolase [EC 3.2.1.98] was discovered in 1971 by K. Kainuma et al. as a cell-bound enzyme. Recently, we found that an ultraviolet-induced mutant from Aerobacter aerogenes (Klebsiella pneumoniae) produced an extracellular exo-maltohexaohydrolase. The mutation was carried out by ultraviolet irradiation to achieve 1% survival. The culture conditions for the production of the extracellular enzyme were investigated. The effects of various additives on the enzyme production were also studied. The enzyme was purified by ammonium sulfate precipitation, DEAE-cellulose column chromatography and Sephadex G-100 gel filtration to 1100 fold of the activity of the original culture liquor. It gave a single band on polyacrylamide disc gel electrophoresis and the molecularV weight by SDS polyacrylamide gel electrophoresis and Sephadex G-100 gel filtration were 65, 000 and 48, 000 respectively. The amylase showed maximum activity at 52°C and pH 7.0. The pH-stability range was relatively wide, the enzyme retaining more than 80% of its initial activity in the range of pH 5.0 to 10.0. It was stable below 50°C and thermostability was improved by the addition of calciumion. The enzyme acted on Q-limit dextrins of amylopectin and glycogen to form branched oligosaccharicles. The characteristics of the enzyme were similar to those of the cell-bound enzyme with a few exceptions.
