Manganese cytochrome c. Structure and properties.

Oxidized and reduced manganese cytochromes c, Mn Cyt c+ and Mn Cyt c, have been synthesized. Mn Cyt c+ and Fe Cyt c+ have identical electrophoretic and ion exchange mobilities. Mn Cyt c+ does not bind F-, CN-, or N3- ions; Mn Cyt c does not bind CO or O2. Mn Cyt c is very rapidly autooxidized by O2 even at -50 degrees. The manganese ion is readily dissociated from Mn Cyt c at acidic pH values. Both Mn Cyt c and Mn Cyt c+ are high spin complexes with 3d5 S = 5/2 and 3d4 S = 2 electronic configurations, respectively. The epr spectrum of Mn Cyt c is rhombic with (formula: see text). Both oxidized and reduced Mn Cyt c react with NO; the former reaction is reversible and the product has the following epr spectral parameters: (formula: see text). There is no superhyperfine interaction observable with the NO ligand, and the unpaired electron density is estimated to be mostly in the metal ion d xy orbital. The structure is best formulated as Mn Cyt c (NO)+. The half-reduction potential of Mn Cyt c is + 60 +/- 40 mV. It is neither oxidized by cytochrome oxidase nor reduced by NADH, NADPH, or succinate cytochrome reductase. These physical, chemical, and enzymic properties of manganese cytochromes c suggest a five-coordinate metalloporphyrin prosthetic group with the manganese ion situated significantly out-of-plane toward the side of His-18.