EPR characterization of R. capsulatus strains carrying the cyt b Lys329Ala, Asp or Arg substitutions. EPR spectra of membranes prepared from wild type (pMTS1/MT-RBC1) Rhodobacter capsulatus strain and its cyt b Lys329Ala, Lys329Asp and Lys329Arg mutant derivatives, as described in Materials and Methods, and reduced with ascorbate (asc) in the absence (black traces) and presence (green traces) of famoxadone (Fam). The gx EPR transitions (g values of 1.8 and 1.78) corresponding to the reduced Fe2S2 cluster of the ISP subunit of cyt bc1 in the absence and presence of the inhibitor famoxadone are indicated by vertical dashed lines. The EPR spectra recording conditions were for all samples: Temperature, 20K; microwave power, 2mW at 9.4GHz; modulation amplitude 10 G at 100 kHz and four scans.