Characterisations of Lactobacillus reuteri SK24.003 glucansucrase: Implications for α-gluco-poly- and oligosaccharides biosynthesis.

Glucansucrase was obtained from Lactobacillus reuteri SK24.003 and its characterizations and in vitro biosynthesis for glucose polymer and oligosaccharides were investigated. The final specific activity of glucansucrase was 1.3IU/mg protein with 8.6-fold purification and 8.7% recovery. The molecular weight of purified enzyme was 166.0kDa. The glucansucrase exhibited optimum activity at 30-35°C, whereas the maximum activity was obtained at pH 5.0-5.5. The double-charged ions including Mg(2+), Mn(2+), Ni(2+), Co(2+), Ca(2+), Fe(2+) and Zn(2+) activated the glucansucrase activities and Ca(2+) ion highly stimulated the activity by approximately 4 times. Km, Vmax and kcat of purified glucansucrase were calculated to be 3.7mM, 0.8IU/mg and 18.21/s, respectively. For in vitro biosynthesis, glucansucrase synthesized 1,6-,1,4-α-d-glucan with a molecular weight of 2.5×10(7)g/mol from sucrose as initial primer. Moreover, maltose acceptor-products synthesized by glucansucrase were composed of panose, maltotriose, maltotetraose, tetrasaccharide and pentasaccharide products analogues with an α-1,4/α-1,6 alternating structure.