Role of transamination in the mobilization of respiratory substrates in germinating seeds of castor oil plants

The metabolism of 1,4-¹⁴C-succinate and 2,3-¹⁴C-succinate and the activity of succinic semialdehyde dehydrogenase (EC 1.2.1.16) were studied in germinating seeds of castor oil plants (Ricinus communis L.). Succinate metabolism involved succinate dehydrogenase and was sensitive to metabolites of the γ-aminobutyric acid shunt. Considerable accumulation of the label in amino acids reflected the progression of transamination reactions. Succinic semialdehyde dehydrogenase was purified from the endosperm of castor oil plants. Kinetic characteristics of the enzyme were evaluated. Our study indicates that the mobilization of respiratory substrates during germination of castor oil plants is related to active transamination of ketoacids in the Krebs cycle and involves the γ-aminobutyric acid shunt.