METABOLISM OF RAFFINOSE AND SUCROSE IN GERMINATING BROAD-BEAN (VICIA FABA) SEEDS

Enzyme preparations from germinating broad-bean seeds can produce UDPG from sucrose or raffinose when incubated with UDP; in the latter case D-galactose is also formed. This observation suggests that raffinose can be metabolized in two stages: (1) the hydrolytic cleavage of the trisaccharide by a-galactosidase with the release of galactose and sucrose; (2) a sucrose: UDP glucosyltransferase (reversed sucrose synthetase)-catalysed transfer of D-glucose from sucrose to UDP. The galactose liberated in stage (I) in Vicia faba seeds can probably be converted to a-D-galactose-1-phosphate by galactokinase. The levels of the glucosyltransferase at various stages of germination have been measured, the enzyme has been partially purified, and an estimate has been made of its apparent molecular weight. The glucosyltransferase is specifically inhibited by D-glucose and D-fructose and the role of this enzyme in catabolic processes is discussed in general terms. © 1969 Oxford University Press.