Reduction of cytochrome c by ferrous ions and ethylenediaminetetraacetic acid in acid solution.

Cytochrome c was reduced by ferrous EDTA over the pH range 0.7 to 5.5, but not by ferrous ions alone. A typical hemochromogen of the low spin type was observed between pH 2.2 and 5.5, but spectra of the high spin type were seen between pH 0.7 and 2.1. CO-Ferrocytochrome c was obtained over the pH range of 1.6 to 3.2 by this method. The spectrum was similar to that of alkaline CO-ferrocytochrome c and two bands in the Soret region were observed at 392 and 413 rnp. o-Phenanthroline, o(, a’-dipyridyl, 8-hydroxyquinoline, or amino acids could not be substituted for EDTA for the reduction of cytochrome c at acid pH. At neutral pH, cytochrome c was fully reduced by a 2-fold molar excess of ferrous ions in the absence of EDTA.