Lack of site-specificity of spinach chloroplast coupling factor 1.

The irreversible inhibition of chloroplast phosphorylation by either sulfate anions, or N-ethylmaleimide, is energy dependent. Chloroplasts must first be illuminated in the presence of the inhibitors and a mediator of electron flow, for the subsequent phosphorylation to show any inhibition. Both inhibitors affect the chloroplast coupling factor 1. Electron transport only through Photosystem I can be used to activate either of these inhibitions. The subsequent inhibition in a second light reaction is the same whether ATP synthesis is supported by Photosystem I, or by Photosystem II electron transport. The reverse experiment, activating inhibition by electron transport only through Photosystem II, is possible in the case of sulfate. Again, the inhibition is expressed whether Photosystem II or Photosystem I electron flow supports ATP synthesis. We conclude that the two electron transport regions of probably generate the same high energy state which is able to activate all members of a functionally uniform coupling factor population. These enzyme molecules must catalyze phosphorylation coupled to electron transport through either region of the chain. The results tend to discredit models requiring a separate group of coupling factor molecules unique to each part of the chain.