Complete analysis of the cytochrome components of beef heart mitochondria in terms of spectra and redox properties. The b-type cytochromes.

The b-cytochromes of beef heart mitochondria have been analyzed by procedures which use optical spectra rather than two points for each cytochrome species. The analytical procedures included first derivatives for background behavior, second derivatives for peak features, and singular value decomposition (Shrager, R.I., and Hendler, R.W. (1982) Anal. Chem. 54, 1147-1152) for the entire spectra. Titrations were performed by electrical oxidation and reduction and by chemical reduction. Four b-cytochromes have been identified in terms of their unique difference spectra, midpoint potentials (Em), and number of electrons transferred (n). They are cytochrome bK, Em = 83 mV, n = 1; cytochrome bT2, Em = -17 mV, n = 2; cytochrome bT1; Em = -95 mV, n = 1; and cytochrome b562L, Em = -146 mV, n = 4. The Em values of cytochromes bT1, bT2, and b562L respond to changes in pH indicating a loss of one proton per oxidation. Antimycin and/or ATP do not affect the spectrum or Em value of any of the cytochromes. An apparent red shift for the absorption maximum of cytochrome bK caused by antimycin may be due to an increased level of reduction of cytochrome bT2.