In this study, lyophilized banana fruits were used as the source of sucrose synthetase (UDP-glucose:D-fructose 2-glucosyltransferase, 2.4.1.13).Extraction by grinding with a buffer containing caffeien and 2-mercaptoethanol yielded a crude extract which could be further purified by fractionation with?ammonium sulfate and adsorption on calcium phosphate gel. It was found that the interfering factors encountered previously such as tannins, pectic substances and polyphenoloxidase could be eliminated by these procedures, and the enzyme with a relatively high activity was obtained. Furthermore, an?activity of sucrose phosphate synthetase (UDP-glucose:D-fructose 6-phosphate 2-glucosyltransferase, 2.4.1.14), which had not yet been demonstrated?in banana fruits before,was alos detected in the crude extract. Partially purified sucrose synthetase from banana fruits was more stable at 0- 4° and at pH values between 6. 0-9.0. The optimum pH of this enzyme for?catalyzing the reaction in the direction of sucrose cleavage was about 6.5.This enzyme showed relatively broad specificities to di- and trisaccharides and to nucleoside diphosphates. No activator for this enzyme was found and heavy?metal ions such as Cu++, Hg++ and Ag+ completely inhibited the enzyme action at a concentration of 4x10-3M. Thiol group reagents including p-mercurcuriben-zoate (PCMB), N-ethylmaleimide and iodoacetic acid showed no or little in-hibitory effect at concentrations normally capable of inhibiting an SH enzyme.The molecular weight determined by the gel filtration technique was about 420,000. It was interesting to compare this data to the sedimentation coefficient(S209w)6.9, which was estimated by a sucrose density gradient ultracentrifugation technique. The Km value of this enzyme for sucrose at standard assay?condition was 6.99x10-2M and the S0.5 value for UDP 0.83x10-4M.The Hill coefficients (n values) estimated from Hill plots were 1.0 and 1.53 for sucrose and UDP respectively, indicating that the enzyme could be an allosteric protein but its binding behavior toward sucrose was different form other known sucrose synthetases.
