Conformation of the axially bound ligands of the heme iron and electronics structure of heme c in the cytochromes c-551 from pseudomonas mendocina and pseudomonas stutzeri and in cytochrome c2 from rhodospirillum rubrum

Abstract

The cytochromes c-551 from Pseudomonas mendocina, c-551 from Pseudomonas stutzeri and c 2 from Rhodospirillum rubrum have been isolated and investigated by 1H-nuclear magnetic resonance at 360 MHz and 500 MHz and by circular dichroism spectroscopy. For all three proteins individual 1H-NMR assignments were obtained for heme c and the axial ligands of the heme iron. The spatial arrangement of the axial ligands in the reduced proteins was determined by nuclear Overhauser enhancement experiments and in the oxidized proteins by CD studies. For the two cytochromes c-551 the axial methionine spatial structure corresponds to S chirality at the iron-bound sulfur atom and coincides closely with the previously established structure of cytochrome c-551 from Pseudomonas aeruginosa. In the cytochrome c 2, R chirality of the axial methionine was observed, and the structure corresponds to that found previously for several mammalian-type cytochromes c and for the cytochromes c-552 from Euglena gracilis and Spirulina maxima. Concomitantly with the different methionine chirality, characteristically different electronic structures were observed for the ferricytochromes c-551 and the ferricytochrome c 2, which coincides with previous observations with cytochromes c from different species.