Mutational analysis and characterization of dextran synthesizing enzyme from wild and mutant strain of Leuconostoc mesenteroides.

Dextransucrase producing Leuconostoc mesenteroides KIBGE IB-22 was subjected to mutagenesis by exposing the strain to UV irradiation. The dextransucrase produced by both the strains (wild and mutant) were characterized and the catalytic properties of both wild and mutant dextransucrase were compared. Among 42 mutants, KIBGE IB-22M20 exhibited 6.75 times increase in dextransucrase activity as compared to the wild one. Wild dextransucrase showed specific activity of 31.3 DSU/mg of protein with V(max) and K(m) of 18.84 DSU/ml/h and 77.09 mM, respectively at 30 °C in 0.3 M citrate buffer (pH 4.5) using sucrose as substrate. Whereas, mutant dextransucrase exhibited a specific activity of 173.2 DSU/mg with V(max) and K(m) values of 104.2DSU/ml/h and 101.7 mM, respectively at 35 °C in 0.3 M citrate buffer (pH 5.0) keeping the same substrate as for wild. Dextransucrase from both wild and mutant showed an approximate molecular weight of 221 kDa by SDS-PAGE.