Properties of aromatic residues in ferricytochrome c3 of desulforvibrio vulgaris Miyazaki F studied by 1H NMR

Conditions for the specific labelling of the tetrahaeme protein cytochrome c 3 of Desulfovibrio vulgaris Miyazaki F during culture of this sulphate-reducing bacterium in a minimal medium were established. Phenylalanine and tyrosine residues were specifically deuterated at more than 85% efficiency. Cytochrome c 3 has nine histidine, three tyrosine and two phenylalamine residues. Eight histidine imidazoles are ligated to four haeme groups. Using the deuterated cytochrome c 3 , aromatic proton signals of phenylalanine and tyrosine residues in the fully oxidized state were identified. However, the signals of one phenylalanine residue were missing and this was tentatively assigned to Phe20. The aromatic proton signals of His67 were also assigned p 2 H titration. Its p k 1 was much higher than that for the free histidine residue. No tyrosine residue was ionized up to p 2 H 12.