Determination of the coordination geometry at the heme iron in three cytochromes c from Saccharomyces cerevisiae and from Candida krusei based on individual 1H-NMR assignments for heme c and the axially coordinated amino acids.

The 1H-NMR lines of heme c and the axial ligands in reduced and oxidized Iso-1 and Iso-2 cytochromes c from Saccharomyces cerevisiae and in cytochrome c from Candida krusei were individually assigned and the conformation of the coordination sphere of the heme iron was investigated with the use of proton-proton Overhauser enhancement measurements and circular dichroism spectroscopy. The coordination geometry of the axial methionine and the axial histidine and the electronic structure of the heme were found to be closely similar in these yeast cytochromes c and in mammalian cytochromes c. In particular, R chirality at the sulfur atom of the iron-bound methionine was observed in both groups of proteins. Additional nuclear Overhauser enhancement studies of the spatial arrangement relative to the heme group of amino acid side-chains in the heme crevice of yeast ferrocytochromes c showed that the conformational homologies extend beyond the immediate coordination sphere of the heme iron. These data provide a conformational basis for observations on the functional properties of cytochromes c from yeast and mammalian species, which were reported previously by other groups.