Substrate specificity of an .ALPHA.-glucosidase in sugar beet seed.

The substrate specificity of sugar beet α-glucosidase was investigated. The enzyme showed a relatively wide specificity upon various substrates, having α-1, 2-, α-1, 3-, α-1, 4- and α-1, 6-glucosidic linkages. The relative hydrolysis velocity for maltose (G2), nigerose (N), kojibiose (K), isomaltose (1), panose (P), phenyl-α-maltoside (φM) and soluble starch (SS) was estimated to be 100:130:10.7:22.6:54.6:55.8:120 in this order; that for malto-triose (G3), -tetraose (G4), -pentaose (G5), -hexaose (G6), -heptaose (G7), -octaose (G8), amyloses (G13) and (G17), 91:91:91:91:80:57:75:73. The Km values for N, K, I, P, φM and SS were 16.7 mat, 1.25mM, 10.8mM, 8.00mM, 4.12mM and 1.90mg/ml, respectively; that for G2, G3, G4, G5, G6, G7, G8, G-13 and G-17 were 20.0mM, 3.67mM, 2.34mM, 0.64mM, 0.42mM, 0.32mM, 0.23mM, 0.36mM and 0.26mM, respectively. The enzyme, though showed higher affinity and activity toward soluble starch than toward maltose, was considered essentially to be an α-glucosidase.