Dextran molecular size and degree of branching as a function of sucrose concentration, pH, and temperature of reaction of Leuconostoc mesenteroides B-512FMCM dextransucrase

Reactions of Leuconostoc mesenteroides B-512FMCM dextransucrase with increasing concentrations of sucrose, from 0.1 to 4.0 M, gave a decreasing amount of high-molecular weight dextran (HMWD) ( > 10(6) Da) with a concomitant increase in low-molecular weight dextran (LMWD) ( < 10(5) Da). At 0.1 M sucrose, pH 5.5, and 28 degreesC, 99.8% of the dextran had a MW > 10(6) Da and at 4.0 M sucrose, 69.9% had a MW < 10(6) Da and 30.1 %,, had a MW > 10(6) Da, giving a bimodal distribution. The degree of branching increased from 5% for 0.1 M sucrose to 16.6% for 4.0 M sucrose. The temperature had very little effect on the size of the dextran, which was > 10(6) Da, but it had a significant effect on the degree of branching, which was 4.8%,, at 4 degreesC and increased to 14.7% at 45 degreesC. Both the molecular weight (MW) and the degree of branching were not significantly affected by different pH values between 4.5 and 6.0. (C) 2003 Elsevier Science Ltd. All rights reserved.