The Productivity of Sucrose-degrading Enzyme by the Sucrose-assimilating Lactic Acid Bacterium Lactobacillus paracasei NRIC0765

Abstract

　The lactic acid bacterium Lactobacillus paracasei NRIC0765can assimilate sucrose well, with no glucose repression activity in the presence of glucose. In this study, we investigated the productivity of the sucrose-degrading enzyme by Lb. paracasei NRIC0765, and analyzed the characteristics of this enzyme. Lb. paracasei NRIC0765 showed high sucrose degrading enzyme productivity in both the presence and absence of sucrose. We purified this sucrose-degrading enzyme using a 4-step chromatographic method. The purified enzyme showed high degrading activity on sucrose, p-nitrophenyl-α-D-glucopyranosid, methyl-α-D-glucoside, ethyl-α-D-glucoside and isomaltose, and the Km values for these substrates were 389, 0.671, 128, 12.5 and 25.5 mM, respectively. The catalytic turnover number for these substrates were 102, 64.1, 34.9, 36.7, and 52.8 s^－1, respectively. Optimum temperature was 40℃, and the activity was stable below 45℃. The activity was maximal at pH 5.0, and the activity was stable in a pH range of 4.0 to 7.0. The molecular mass was estimated to be 66 kDa, and the isoelectric point was estimated to be 5.55. The N-terminal amino acid sequence of this enzyme showed high homology to oligo-1, 6-glucosidase and exo-α-1, 4-glucosidase enzymes of some Lactobacillus and Bacillus strains.