Production of Lactosucrose by Bacillus natto Levansucrase and some Properties of the Enzyme.

Abstract

Lactosucrose (O-beta-D-Gal(p)-(1 --> 4)-O-alpha-D-Glc(p)-(1 --> 2)-beta-D-Frc(f)) was produced from the mixture of sucrose and lactose by Bacillus natto levansucrase [EC 2.4.1.10]. The enzyme was purified by precipitation with ammonium sulfate and chromatographies on Butyl-Toyopearl 650 M and DEAE-Toyopearl 650 S. Molecular weight of the enzyme was estimated to be 55 kDa in SDS-polyacrylamide gel electrophoresis, with its isoelectric point at pH 4.9. Optimum pH and temperature were 6.2 and 35-degrees-C, respectively. The enzyme was stable from pH 5.5 approximately 7.0 and up to 35-degrees-C. The activity was inhibited by metal ions such as Cu2+, Ag+, and Hg2+. The kinetics for lactosucrose formation was explained by the ping-pong mechanism with 0.21 M for sucrose and 0.42 M for lactose as Km values. In the immobilized enzyme, lactosucrose production was reduced, whereas levan production was promoted compared with those in the native enzyme.