Preparation and Characterization of a Pentaammineruthenium(III) Derivative of Horse Heart Ferricytochrome c

A stable complex between pentaammineruthenium(III) and histidine-33 in horse heart ferricytochrome c is formed in the reaction between aquopentaammineruthenium(II) and the protein at pH 7. HPLC of the tryptic hydrolysate of the modified protein was employed to identify the pentaammineruthenium binding site. Spectroscopic measurements show that the integrity of the native structure in the vicinity of the heme c group is maintained in the ruthenium-modified protein. The reduction potentials are: heme c (Fe3+/2+), 0.26 V; Ru(NH3)5(His-33)$^{3+/2+}$, 0.15 V (vs. normal hydrogen electrode).