THE THERMODYNAMIC CHARACTERISTIC OF 4-HEME CYTOCHROME-C IN RHODOPSEUDOMONAS-VIRIDIS REACTION CENTERS, AS DERIVED FROM A QUANTITATIVE-ANALYSIS OF THE DIFFERENTIAL ABSORPTION-SPECTRA IN ALPHA-DOMAIN

A method of decomposing of the absorption spectrum of four-heme cytochrome of a Rhodopseudomonas viridis reaction center preparation into spectra of individual components was used to estimate the degree of the reduction of hemes as a function of redox potential in the medium. The method enables an evaluation of the shape of redox-titration curves of each heme. The redox-titration curves derived by this approach are approximated well by a Nernst equation with n = 1 and Em-values of 360 mV, 312 mV, 20 mV and less than -50 mV. For all of the redox species the values of midpoint potential estimates by the above method are in good agreement with those determined earlier using another procedure [Dracheva et al. (1988) Eur. J. Biochem. 171, 253-264]. The accuracy of deconvolution of data is within the experimental errors of the redox potential measurement. © 1990.