Magnetic Studies on the Ferri‐haem Undecapeptide of Cytochrome c

Abstract
The pH-dependence of the magnetic moment of a ferri-heme undecapeptide, produced by peptic digestion of cytochrome c [horse heart] was measured in aqueous solution using a NMR method. Below pH 3 the magnetic moment is consistent with the presence of hydroxo-bridged dimers of high-spin Fe(III). Above pH 7 the Fe(III) is low-spin, the spin crossover conforming to a simple titration curve with pK 6.3 (n = 1). This transition is discussed with reference to spectrophotometric studies of ligand binding at the heme.