Proton‐NMR studies show that the Thr‐102 mutant of yeast iso‐1‐cytochrome c is a typical member of the eukaryotic cytochrome c family

The Thr‐102 mutant of yeast iso‐1‐cytochrome c is a useful system for the study of structure‐function relationships in this important class of electron transfer proteins, but little is known about its structure. Furthermore, few assignments of individual amino acid residues in yeast iso‐1‐cytochrome c have been made by proton NMR. Here we report assignments for nearly half of the amino acids in the reduced Thr‐102 mutant of yeast iso‐1‐cytochrome c . We also report assignments for the oxidized Thr‐102 mutant. While the crystal structure of the reduced iso‐1‐cytochrome c (N. B. not the Thr‐102 mutant) has been reported, there is currently little structural information concerning its solution structure and none concerning the oxidized protein. There is also no information concerning the structure of either oxidation state of the Thr‐102 mutant. Comparison of the chemical shift and NOE data for the reduced Thr‐102 mutant and comparison of paramagnetic shifts for analogous residues between this mutant and horse‐heart and tuna cytochromes c reveal that both the basic fold of Thr‐102 yeast iso‐1‐cytochrome c and the region around the site of the mutation are the same as those found in the latter two proteins. It is concluded that the results from structure function studies using the Thr‐102 mutant will be applicable to eukaryotic cytochrome c in general. This knowledge allows us to proceed to a description of some mutants of yeast iso‐1‐cytochrome c in the next paper.