Fatty acid synthesis by spinach chloroplasts I. Property of fatty acid synthesis from acetate

Abstract

Intact chloroplasts (about 70% Class I chloroplasts) isolated from spinach leaves incorporated 150 nmoles of [1-C] acetate into fatty acids per mg chlorophyll in 1 hr at pH 8.3, 25°C and 25,000 lux. On electron and phase-contrast microscopies combined with hypotonic treatment of chloroplasts, this synthetic activity was shown to be proportional to the percentage of Class I chloroplasts in the preparation. Light was necessary for the synthesis, the activity in the complete reaction mixture in the dark being only 2% of that in the light. The synthetic activity increased with increasing intensities of light to reach saturation at 6,000 lux. CoA and ATP were most effective as cofactors, HCO3-, HPO4 -, Mg and Mn were less effective. ATP could be replaced by ADP in the presence of Pi, suggesting possible supply of ATP by photophosphorylation. Omission of the NADPH-generation system and NADH did not affect the synthesis, indicating sufficient provision of endogenous NADPH and NADH in intact chloroplasts under light. Addition of DTE did not cause recovery of the synthetic activity of intact chloroplasts in the dark.