High-energy Forms of Cytochrome b

Abstract

SUB-MITOCHONDRIAL particles prepared from horse or ox heart contain two species of cytochrome b in equal amounts, one (b_i) affected by antimycin and the other (b) not affected^1–3. In addition to its well known inhibitory effect on the respiratory chain, acting between cytochromes b and c₁, antimycin brings about an increased reduction of the total cytochrome b present in sub-mitochondrial particles and causes a shift in absorption of 1–2 nm towards longer wavelengths of the b band. This “redshift” is best studied with the wavelength pair 566–560 nm, for the absorption maximum of ferrocytochrome b is at 563 nm, and A_{566–560 nm} is not affected by the redox state of cytochrome b (ref. 1). Sigmoidal curves for the antimycin effect are found with sub-mitochondrial particles⁴ and with intact white potato (W. D. Bonner and E. C. S., unpublished) or rat heart (H. J. W., J. A. B. and E. C. S., unpublished) mitochondria in the presence of uncoupler, and linear (or hyperbolic) with energized mitochondria (state 4). To explain these antimycin effect curves, it is proposed that antimycin, a multi-site inhibitor in particles, reacts preferentially with and stabilizes a high-energy form of cytochrome b_i (b_i∼X) (refs. 4 and 5).