REPLACEMENT OF LYSINE-45 BY UNCHARGED RESIDUES MODULATES THE REDOX-BOHR EFFECT IN TETRAHEME CYTOCHROME C(3) OF DESULFOVIBRIO-VULGARIS (HILDENBOROUGH)

The structural basis for the pH dependence of the redox potential in t he tetrahemic Desulfovibrio vulgaris (Hildenborough) cytochrome c(3) w as investigated by site-directed mutagenesis of charged residues in th e vicinity of heme I. Mutation of lysine 45, located in the neighborho od of the propionates of heme I, by uncharged residues, namely threoni ne, glutamine and leucine, was performed. The replacement of a conserv ed charged residue, aspartate 7, present in the N-terminal region and near heme I was also attempted. The analysis of the redox interactions as well as the redox-Bohr behavior of the mutated cytochromes c(3) al lowed the conclusion that residue 45 has a functional role in the cont rol of the pK(a) of the propionate groups of heme I and confirms the i nvolvement of this residue in the redox-Bohr effect.