Solution structure of reduced horse heart cytochrome c

In the frame of a broad study on the structural differences between the two redox forms of cytochromes to be related to the electron transfer process, the NMR solution structure of horse heart cytochrome c in the reduced form has been determined. The structural data obtained in the present work are compared to those already available in the literature on the same protein a nd the presence of conformational differences is discussed in the light of the experimental method employed for the structure determination. Redox-sta te dependent changes are analyzed and in particular they are related to the role of propionate-7 of the heme. Also some hydrogen bonds are changed upo n reduction of the heme iron. A substantial similarity is observed for the backbone fold, independently of the oxidation state. At variance, some mean ingful differences are observed in the orientation of a few side chains. Th ese changes are related to those found in the case of the highly homologous cytochrome c from Saccharomyces cerevisiae. The exchangeability of the NH protons has been investigated and found to be smaller than in the case of t he oxidized protein. We think that this is a characteristic of reduced cyto chromes and that mobility is a medium for molecular recognition in vivo.