Potentiometric and optical resolution of cytochromes c and c 1 in purified mitochondria from higher plant tissue, solanum tuberosum

Abstract

Mitochondrial cytochromes c and c1 have long been considered indistinguishable from a potentiometric point of view. By combining rapid scan spectrometry to run redox titrations with numerical analysis using a generalized Nernst equation, it was possible to resolve cytochrome c and c1 midpoint potentials in yeast and mushroom mitochondria. In the reported work, this approach has been applied to purified mitochondria from higher plant tissue (Solanum tubersosum L.). The rapid scan spectrometric technique provided clear evidence of reversible base line changes monitored by redox potential changes. The basic mechanism responsible for this modification in the mitochondria optical properties remains to be defined. However, we suggest that this phenomenon could play a regulatory role in the overall electron transfer process. It is necessary to make an initial correction of the recorded spectra prior to numerical analysis. When this is done, two midpoint potential values are resolved by running analyses in the 550–555 nm range: 283±3 m V and 213±11 m V. They are identical to the ones found for cytochromes c and c1 in yeast and mushroom mitochondria. The individual difference α bands were resolved by running analyses at each wavelength of the corrected spectra, the resolved midpoint potentials being kept fixed. This approach, the only one to date which has succeeded in resolving mitochondrial cytochrome c and c1 midpoint potentials, is discussed with respect to other methods. Limitations are pointed out.