1H NMR studies of the electron exchange between cytochrome c and iron hexacyanides. Definition of the iron hexacyanide binding sites on cytochrome c.

Binding of [Fe(CN)6]3-, [Cr(CN)6]3-, [Co(CN)6]3- and [Cr(C2O4)3]3- to horse, tuna and Candida krusei cytochromes c has been studied by high-resolution 1H NMR spectroscopy. All the reagents bind at the same sites. There are at least two binding sites, and probably three, on horse cytochrome c at pH 7. One of the sites is only a weak binding site and is far from the haem group, whereas the other site(s) is(are) at the haem crevice. Ka for binding of [Fe(CN)6]3- to trimethyllysine-72 of C. krusei ferricytochrome c is 140 +/- 15 M-1 at 27 degrees C and pH 7.