Altered absorption spectra of iso-1-cytochromes c from mutants of yeast.

Low temperature (-190 degrees) spectrophotometric recordings were made of mutant strains of the yeast Saccharomyces cerevisiae containing various altered sequences of iso-1-cytochromes c. All mutants with replacements of the tryptophan 64 residue had abnormal Calpha-bands, in which the alpha2-peaks were accentuated to various degrees by being more separated from the major alpha1-peaks and by making up a larger portion of the total Calpha-peak. The altered iso-1-cytochromes c included those having the normal tryptophan 64 replaced by phenylalanine, leucine, tyrosine, cysteine, serine, or glycine as well as those having replacements at position 64 and additional replacements at other sites. Tryptophan 64 in iso-1-cytochrome c, which corresponds to tryptophan 59 in vertebrate cytochromes c, appears to be an important residue for preserving the electronic environment of the heme group. It is uncertain, however, whether altered spectra are due specifically to the abnormal residues at position 64 or due to distorted tertiary structures caused by the replacements.