Etude de la photophosphorylation endogene des chloroplastes isoles d'epinardStudy on endogenous photophosphorylation of isolated spinach chloroplasts

Whole spinach chloroplasts were able to perform photophosphorylation under nitrogen without the addition of any redox cofactor. This “endogenous” phosphorylation was totally insensitive to 3-(p-chlorophenyl)-1,1-dimethylurea. After osmotic shock endogenous ATP formation decreased but the addition of 3-(p-chlorophenyl)-1,1-dimethylurea stimulated it.

Under a stream of nitrogen, whole chloroplasts reduced NADP⁺ after an osmotic shock, in the absence of added ferredoxin. The resulting ATP/NADPH ratios were high (approx. 2 or 3). They decreased to 1 in the presence of either exogenous ferredoxin, 3-(p-chlorophenyl)-1,1-dimethylurea or limiting light: i.e. high ATP/NADPH ratios were observed only when the terminal step of NADP⁺ reduction was limiting.

The endogenous anaerobic phosphorylation was inhibited by antimycin A to the same extent as the O₂-dependent endogenous non-cyclic phosphorylation.

A direct inhibition of electron transport by antimycin A has never been observed.