HORSE HEART CYTOCHROME C-LOCAL STRUCTURE IN SOLUTION - CONFORMATIONAL-ANALYSIS BY 2-DIMENSIONAL NUCLEAR OVERHAUSER EFFECT SPECTROSCOPY DATA

The backbone conformations of the horse heart cytochrome c in the oxidized (ferricytochrome c) and reduced (ferrocytochrome c) states were calculated by two-dimensional nuclear Overhauser effect spectroscopy data [5, 6] using a method worked out previously [1-4]. The secondary structure elements were detected for both protein forms and the conformations of the irregular polypeptide chain segments were analyzed. When the conformations of the ferri- and ferrocytochrome c were compared in solution, their secondary structures were similar. Small differences in the conformations of the two forms of molecules localized on polypeptide chain fragments situated in its spatial structure close to the heme cavity were observed. When the dihedral-phi and psi-angles of the calculated horse cytochrome c conformations were compared to respective characteristics of x-ray structures of tuna ferri- and ferrocytochrome c made for the oxidized and reduced forms of the protein by quantitative criteria, the similarity of their conformations in solution and in the crystal form were shown. Conformational changes of individual amino acid residues which take place during the solution-to-crystal transition occur on the surface fragments of protein globules and do not lead to significant changes in the secondary structure of the molecule.