title: Electron transport pathways in spinach chloroplasts. Reduction of the primary acceptor of photosystem II by reduced nicotinamide adenine dinucleotide phosphate in the dark.
abstract: Addition of NADPH to osmotically lysed spinach chloroplasts results in a reduction of the primary acceptor (Q) of photosystem II. This reduction of Q reaches a maximum of 50% in chloroplasts maintained under weak illumination and requires added ferredoxin and Mg2+. The reaction is inhibited by (I) an antibody to ferredoxin-NADP+ reductases (EC 1.6.7.1), (ii) treatment of chloroplasts with N-ethylmaleimide in the presence of NADPH, (iii) disulfodisalicylidenepropanediamine, (iv) antimycin, and (v) acceptors of non-cyclic electron transport. Uncouplers of phosphorylation do not affect NADPH-driven reduction of Q. It is proposed that electron flow from NADPH to Q may occur in the dark by a pathway utilising portions of the normal cyclic and non-cyclic electron carrier sequences. The possible in vivo role for such a pathway in redox poising of cyclic electron transport and hence in controlling the ATP/NADPH supply ratio is discussed.
mesh_terms: D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003624:Darkness; D004229:Dithiothreitol / Q000494:pharmacology; D004579:Electron Transport; D005287:Ferredoxin-NADP Reductase / Q000378:metabolism; D005288:Ferredoxins / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000187:drug effects; D010944:Plants; D013050:Spectrometry, Fluorescence
chemical_list: D005288:Ferredoxins; D009249:NADP; D005287:Ferredoxin-NADP Reductase; D008274:Magnesium; D004229:Dithiothreitol