A re-examination of 5-aminolevulinic acid synthesis by isolated intact, developing chloroplasts: The O 2 requirement in the light

Abstract

Synthesis of 5-aminolevulinic acid (ALA) in organello was re-examined with developing chloroplasts isolated from greening cucumber ( Cucumis sativus L. var. Beit Alpha) cotyledons. In the dark, ALA accumulated in the presence of ATP, reducing power (NADPH and glucose-6-phosphate), glutamate and levulinic acid (or 4,6-dioxoheptanoic acid). Under continuous illumination there was no requirement for added ATP and reducing power, unless DCMU was added or O 2 was removed, indicating that ATP and reducing power could be supplied endogenously by photosynthesis in the presence of O 2. No mitochondrial involvement could be demonstrated in this system. Under anaerobic conditions in the light oxaloacetic acid (OAA) could replace O 2 and permit a high accumulation of ALA. The fact that OAA could replace O 2 suggests that an acceptor of non-cyclic electron flow may be required to provide ATP or some other cofactor of ALA synthesis. The phosphorylation uncoupler, 2,4-dinitrophenol, inhibited ALA synthesis. Light-dependent ALA in air was strongly inhibited by methylene blue (MB) and NaN 3, but only very slightly by KCN.