Inhibition of photophosphorylation by phenazine methosulfate.

Phenazine methosulfate was shown to be a competitive inhibitor of H+ in light-induced H+ transport as well as a competitive inhibitor of orthophosphate in photophosphorylation. Similarly, H+, NH4+, and Pi in the presence of adenosine diphosphate were shown to inhibit competitively light-induced binding of phenazine methosulfate to chloroplasts. Pi, in the absence of ADP or other anions such as acetate, partially inhibits light-induced binding of phenazine methosulfate to chloroplasts. However, this inhibition requires a high concentration of the anions. These observations strengthen the concept, previously proposed, that the energetic event in phosphorylation is the removal of the hydrogen atom, as a proton, from Pi by a light-induced nonspecific anionic site or sites within chloroplasts.