Comparative studies of monohemic bacterial C-type cytochromes. Redox and optical properties of Desulfovibrio desulfuricans Norway cytochrome C553(550) and Pseudomonas aeruginosa cytochrome C551.

Redox properties of cytochrome c553(550) from Desulfovibrio desulfuricans Norway (Eo' = 0.04 + 0.02 V/NHE) and cytochrome c551 from P. aeruginosa (Eo = 0.25 +/- 0.02 V/NHE) are compared with those of some monohemic c-type cytochromes. The pK value for the equilibrium between the pH-dependent forms of cytochrome c553(550) (pK = 10.3 +/- 0.1) has been also determined. It is to be noted that the difference between redox potentials can extend to nearly 250 mV, though the axial heme ligands are identical. Structural reasons have to be invoked to explain these variations.