TYROSINE-64 OF CYTOCHROME-C(553) IS REQUIRED FOR ELECTRON-EXCHANGE WITH FORMATE DEHYDROGENASE IN DESULFOVIBRIO-VULGARIS HILDENBOROUGH

Replacement of tyrosine 64 by alanine in cytochrome c(553) from Desulf ovibrio vulgaris Hildenborough prevents electron transfer with the for mate dehydrogenase. Biophysical and biochemical studies show that the protein is correctly folded and that the oxidoreduction potential is n ot modified. The solution structure of the mutant cytochrome determine d by two-dimensional (2D) NMR clearly establishes that the overall fol d of the molecule is nearly identical to that of the wild-type cytochr ome. The electrostatic surface charge distributions for the wild-type and mutant cytochrome are similar, suggesting that the interaction sit e of the physiological partners is not modified by the mutation. The l ack of the aromatic ring induces slight destabilization of the hydroph obic core of the molecule and modifications of the hydrogen bond at po sition 64, as well as conformational disorder of the side chain of K63 . The loss of the hydrogen bond from tyrosine 64 and the increase of t he solvent exposure of the heme are probably responsible of the loss o f electron transfer between formate dehydrogenase and cytochrome c(553 ).