The Metabolism of Raffinose and Sucrose in Germinating Broad-Bean (Vicia faba) Seeds

Enzyme preparations from germinating broad-bean seeds can produceUDPG from sucrose or raffinose when incubated with UDP; in thelatter case D-galactose is also formed. This observation suggeststhat raffinose can be metabolized in two stages: (1) the hydrolyticcleavage of the trisaccharide by a-galactosidase with the releaseof galactose and sucrose; (2) a sucrose: UDP glucosyltransferase(reversed sucrose synthetase)-catalysed transfer of D-glucosefrom sucrose to UDP. The galactose liberated in stage (I) inVicia faba seeds can probably be converted to a-D-galactose-1-phosphateby galactokinase. The levels of the glucosyltransferase at variousstages of germination have been measured, the enzyme has beenpartially purified, and an estimate has been made of its apparentmolecular weight. The glucosyltransferase is specifically inhibitedby D-glucose and D-fructose and the role of this enzyme in catabolicprocesses is discussed in general terms.