Fat metabolism in higher plants XX. relation of fatty acid synthesis and photophosphorylation in lettuce chloroplasts

Abstract

The incorporation of acetate into chloroplast lipids by illuminated chloroplasts in the presence of CoA, HCO 3-, Mg 2+, and Mn 2+, is stimulated by TPN when ADP and orthophosphate are present. p-Chlorophenyldimethylurea and NH 4+, inhibitors of photophosphorylation reactions, also decrease acetate incorporation. The system shows a requirement for orthophosphate. These results are interpreted to mean that acetate incorporation into fatty acids of chloroplasts depends on non-cyclic photophosphorylation which results in the formation of TPNH 2, ATP, and O 2. Cyclic photophosphorylation alone by which only ATP is photoproduced was not found to stimulate acetate incorporation. Acetate incorporation is increased when the reaction is carried out in air instead of nitrogen. The effect is more pronounced in the absence of TPN. These results are explained by the ability of oxygen to catalyze a non-cyclic photophosphorylation, and (or) by the role of oxygen as a cofactor in the synthesis of unsaturated fatty acids. Added TPNH 2, ATP and O 2 were not found to stimulate acetate incorporation in the dark.