A glucosyltransferase which catalyzes the conjugation of ace-tone cyanohydrin to glucose in the last step of linamarin biosynthesis was isolated from young leaves of cassava (Manihot esculenta Crantz.). The glucosyltransferase was found to be a soluble enzyme and was partially purified by 40-80% ammonium sulphate fractionation followed by Sephadex G-200 column and Mono Q HR 5/5 column chromatography. These steps resulted in a purification of 6 folds. The partially purified glucosyltransferase possessed negligible linamarase and little UDP-glucose hydrolysis activity. The native molecular weight of cassava glucosyltransferase was 46,000. The partially purified preparation consisted of five major bands of 13,000

21,000

25,000

31,000 and 39,000 separated by polyaccrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The enzyme activity was unstable but could be kept at -20 degree C for 17 days with 50% loss of the activity. Catalytically, the partially purified glycosyl transferase showed a pH optimum of 9 to 10 and a temperature optimum of 37 degree C. The substrate specificities were also analyzed. UDP-glucose was the best sugar donor with a K(,M) of 0.04 mM which ADP-glucose was not and UDP-galactose was only half as good as UDP-glucose. Among the sugar acceptors tested, acetone cyanohydrin was the best and better than butanone cyanohydrin. Other aliphatic alcohols were poorer sugar acceptors in the following order: isopropanol, butanol, ethanol and glycerol. Phenol was unable to serve as the sugar acceptor for this enzyme. The enzyme was unable to catalyze the transfer of glucose from UDP-glucose to starch, linamarin or simple sugars i.e. glucose, galactose and sucrose. However, a high glucosyltransferase activity was detected in the presence of UDP-glucose and fructose with a K(,m) for fructose of 4.4 mM. This activity could be due either to a contaminating UDP-glucose: D-fructose-glucosyltransferase or to cassava glucosyltransferase having two activities, one for linamarin synthesis and the other for sucrose synthesis.