Fat Metabolism in Higher Plants

Spinach chloroplasts with intact outer envelopes (Class I) rapidly synthesize oleic and palmitic acids from 14C-acetate in the presence of coenzyme A, sodium bicarbonate, magnesium ion, and light. Light intensity studies reveal a 2-fold stimulation at 10 foot-candles and a 10-fold stimulation at 3000 foot-candles. Very low concentrations of detergents (Triton X-100 at 130 µm concentration) greatly stimulate 14C-acetate incorporation and markedly increase the oleic to palmitic ratio (from 1 to 1.5 to over 11). Low concentrations of ATP (2 mm) return the oleic to palmitic ratio to values of 1 to 1.5. Other nucleoside triphosphates are ineffective. Cyanide (0.1 mm) is only partially inhibitory for oleic acid synthesis. Action spectra studies indicate that 14C-acetate incorporation into fatty acids follows the absorption spectrum of chloroplasts.