α-グルコシダーゼの諸性質と基質特異性

木村 淳夫, 竹西 繁行, 高田 益宏, 辻坂 好夫, 千葉 誠哉

doi:10.11541/jag1994.44.303

Aspergillus niger α-glucosidase was crystallized by acetone addition after ammonium sulfate fractionation and chromatographies on DEAE-Sepharose CL-6B and Bio-Gel P-150 (1st and 2nd) columns. The crystalline α-glucosidase, which was a glycoprotein containing 27% carbohydrate as glucose, gave a single band on polyacrylamide disc gel electrophoresis. The molecular weight was estimated to be about 12.0 × 10⁴ by SDS-polyacrylamide disc gel electrophoresis. However, the enzyme consisted of two components (Mr, 4.2 × 10⁴ and 9.0 × 10⁴ ) separable by reversed-phase HPLC causing irreversible inactivation. Their N-terminal sequences were analyzed to be LXPAPSQ and SQDYISL. The optimum pH was 4.5. In the initial reaction stage, phenyl α-maltoside was cleaved into α-glucose and phenyl α-glucoside. The ratios of the maximum velocities (Km values, in parentheses, mM of nonreducing terminal) for maltose, malto-triose, -tetraose, -pentaose, -hexaose, -heptaose and -octaose, maltodextrin (DP= 17), kojibiose, nigerose, isomaltose, phenyl α-glucoside, phenyl α-maltoside, panose and soluble starch were estimated to be 100 (1.30), 122 (1.20), 105 (1.32), 106 (2.09), 108 (3.85), 107 (5.64), 107 (6.02), 103 (20.8), 34.4 (6.76), 78.5 (20.0), 45.4 (9.80), 9.42 (1.82), 110 (1.49), 41.1 (4.88) and 111 (7.14), respectively. The enzyme also hydrolyzed α-glucans such as soluble starch, however, the rates of cleavage were very slow.

α-グルコシダーゼの諸性質と基質特異性

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α-グルコシダーゼの諸性質と基質特異性

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