Fat Metabolism in Higher Plants. XXXVII. Characterization of the beta-Oxidation Systems From Maturing and Germinating Castor Bean Seeds

In the maturing castor bean seed (Ricinus communis), maximum β-oxidation appears at 28 days after flowering and in the germinating seed, 4 days after germination. Highest specific activities for both β-oxidation systems and their component enzymes are associated with cytosomal particles banding at a density of 1.25 g/ml in a sucrose gradient. Substrate specificity studies indicate that of several fatty acids, ricinoleate is oxidized most rapidly by the preparation from the maturing seed (28 days after flowering) while palmitate and linoleate are oxidized most rapidly by extracts obtained from tissue germinated for 4 days. The β-oxidation activities observed in both systems reflect the expression of activity of at least 3 of the component enzymes, crotonase, β-hydroxyacyl dehydrogenase and β-keto-thiolase, which rise and fall co-ordinately. Acyl thiokinase does not appear to play a limiting role in regulating β-oxidation per se under the conditions employed here.