Comparative Study of Photophosphorylation Coupling Factor · Ligand Complex by Circular Dichroism and Chemical Isolation

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Abstract
1. The interaction between the protein coupling of photophosphorylation and its substrate ADP is studied comparatively by two methods: circular dichroism and chemical isolation of the ligand · enzyme complex.2. Experiments with 14C‐labelled ADP indicate that the amount of bound nucleotide is proportional to a variation of the circular dichroism spectrum around 260 nm. When coupling factor is saturated with ADP, two moles of ADP are bound per mole of coupling factor.3. The fixation of ADP on coupling factor is inhibited by the presence, in the incubation medium, of phosphate (Pi), pyrophosphate (PPi) or tripolyphosphate ions. The incubation of coupling factor with [32P]PPi shows that PPi inhibition is due to its fixation on the coupling factor. When coupling factor is saturated, two moles of PPi are bound per mole of coupling factor.