title: Mutation-induced perturbation of the cytochrome c alkaline transition.
abstract: The possible influence of residue Phe-82 in the cytochrome c alkaline isomerization has been evaluated by spectrophotometric pH titrations of a family of mutant yeast iso-1-cytochromes c in which the identity of the residue at this position has been varied. The pKa for the exchange of the Met-80 heme iron ligand was determined from pH titrations in which the S----Fe charge-transfer band (695 nm) was monitored and was found to be 8.5 for the wild type, 7.7 for Ser-82, 7.7 for Gly-82, 7.2 for Leu-82, and 7.2 for Ile-82. pH-jump experiments [Davis et al. (1974) J. Biol. Chem. 249, 2624] established that substitutions at position 82 affect the alkaline isomerization by lowering the pKa of the titrating group by as much as 1.4 pK units; for the Ser-82 and Gly-82 variants, there is also a small effect on the Keq for the ligand exchange equilibrium. On the basis of these findings, we conclude that one critical role for Phe-82 in the wild-type protein is stabilization of the native heme binding environment.
authors.affiliation: Department of Biochemistry, University of British Columbia, Vancouver, Canada.
authors.forename: L L
authors.initials: LL
authors.lastname: Pearce
authors.forename: A L
authors.initials: AL
authors.lastname: Gärtner
authors.forename: M
authors.initials: M
authors.lastname: Smith
authors.forename: A G
authors.initials: AG
authors.lastname: Mauk
mesh_terms: D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D006418:Heme