Complex formation between ferredoxin triphosphopyridine nucleotide reductase and electron transfer proteins.

Ferredoxin-triphosphopyridine nucleotide reductase (FTR) forms complexes with spinach ferredoxin, bacterial ferredoxin, rubredoxin, and flavodoxin. The protein-protein interactions are complete within 3 msec after mixing and the resulting complex contains 1 molecule of FTR and 1 molecule of electron carrier. Complex formation causes changes in the visible spectrum. The complexes are sensitive to ionic strength; they are completely dissociated at high ionic strength. The effect of ionic strength on a catalytic assay involving FTR and these electron carriers suggests that the complexes are important catalytically. The calculated values for AF’, AH’, and AS' and the sensitivity of the complexes to ionic strength suggest that the interactions are mainly hydrophilic in nature. TPN also causes perturbations in the visible spectrum of FTR. The changes are qualitatively and quantitatively different from those obtained with the protein electron carriers. Formation of the difference spectrum is affected by ionic strength, although the effect is less marked than in the protein-protein complexes. The initial changes, which occur rapidly, are followed by a slower first order decay to a second species.