Effect of oxidation state of plastocyanin on the remote binding site pKa

Abstract

The variation of rate constants for the [Co(phen)₃]²⁺[phen = 1,1 0-phenanthroline), [Co(terpy)₂]²⁺(terpy = 2,2′;6′,2″-terpyridine), and [Ru(NH₃)₅(py)]²⁺(py = pyridine) reductions of parsley plastocyanin PCu(II) with pH indicate an acid dissociation pK_a at the remote east face of 5.05, whereas for the oxidant [Co(phen)₃]³⁺ with PCu(I) the value is 5.8. Implications of this change and the relevance to the reaction with cytochrome f are considered.