IDENTIFICATION AND CHARACTERIZATION OF THE EXTRACELLULAR SUCRASES OF ZYMOMONAS-MOBILIS UQM-2716 (ATCC-39676)

An investigation was conducted to isolate, and characterise the extrac ellular sucrases of Zymomonas mobilis UQM 2716. Levansucrase (EC 2.4.1 .10) was the only extracellular sucrase produced by this organism. Thi s enzyme was responsible for sucrose hydrolysis, levan formation, and oligosaccharide production. It had a molecular mass of 98 kDa, a Micha elis constant (K-m) of 64 mM, and a pH optimum of 5.5. It was inhibite d by glucose, but not by fructose, ethanol, sorbitol, NaCl, TRIS or et hylenediaminetetraacetic acid (EDTA). The formation of levan was the p rincipal reaction catalysed by this enzyme at low temperatures. Howeve r, levan formation was thermolabile, being irreversibly lost when leva nsucrase was heated to 35 degrees C. This did not effect sucrose hydro lysis or oligosaccharide formation, which were optimal at 45 degrees C . Sucrose concentration greatly influenced the type of acceptor molecu le used in the transfructosylation reactions catalysed by levansucrase . At low sucrose concentration, the predominant reaction catalysed was the hydrolysis of sucrose to free glucose and fructose. At high sucro se concentrations, oligosaccharide production was the major reaction c atalysed.