Characterization of the Different Dextransucrase Activities Excreted in Glucose, Fructose, or Sucrose Medium by Leuconostoc mesenteroides NRRL B-1299

When grown in glucose or fructose medium in the absence of sucrose, Leuconostoc mesenteroides NRRL B-1299 produces two distinct extracellular dextransucrases named glucose glucosyltransferase (GGT) and fructose glucosyltransferase (FGT). The production level of GGT and FGT is 10 to 20 times lower than that of the extracellular dextransucrase sucrose glucosyltransferase (SGT) produced on sucrose medium (traditional culture conditions). GGT and FGT were concentrated by ultrafiltration before sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Their molecular masses were 183 and 186 kDa, respectively, differing from the 195 kDa of SGT. The structural analysis of the dextran produced from sucrose and of the oligosaccharides synthesized by acceptor reaction in the presence of maltose showed that GGT and FGT are two different enzymes not previously described for this strain. The polymer synthesized by GGT contains 30% α(1→2) linkages, while FGT catalyzes the synthesis of a linear dextran only composed of α(1→6) linkages.

当在无蔗糖的葡萄糖或果糖培养基中培养时，肠膜明串珠菌（Leuconostoc mesenteroides）NRRL B-1299可产生两种不同的胞外葡聚糖蔗糖酶，分别命名为葡萄糖糖基转移酶（glucose glucosyltransferase，GGT）与果糖糖基转移酶（fructose glucosyltransferase，FGT）。GGT与FGT的产酶水平相较于在蔗糖培养基（传统培养条件）中产生的胞外葡聚糖蔗糖酶蔗糖糖基转移酶（sucrose glucosyltransferase，SGT）低10~20倍。在开展十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（sodium dodecyl sulfate-polyacrylamide gel electrophoresis，SDS-PAGE）分析前，通过超滤法对GGT与FGT进行浓缩。二者的相对分子质量分别为183 kDa与186 kDa，与SGT的195 kDa存在差异。通过对蔗糖合成的葡聚糖以及麦芽糖存在下受体反应合成的寡糖进行结构分析，结果证实GGT与FGT为该菌株此前未被报道过的两种不同酶。GGT合成的聚合物含有30%的α(1→2)糖苷键，而FGT则催化合成仅由α(1→6)糖苷键构成的直链葡聚糖。