Physicochemical Properties of Bakers' Yeast Iso-1-cytochrome c

• Published in: The Journal of biological chemistry 1969-07, Vol.244 (14), p.3773-3778
• Main Authors: Aviram, I, Schejter, A
• Format: Article
• Language: English
• Subjects: Animals; Cyanides; Cytochromes; Heme; Horses; Hydrogen-Ion Concentration; Kinetics; Saccharomyces; Species Specificity; Spectrophotometry; Temperature; Thermodynamics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(17)36417-7

A comparison was made of some physicochemical properties of yeast iso-1-ferricytochrome c and the horse protein. Two heme-linked ionizations of yeast iso-1-ferricytochrome c were followed spectrophotometrically. A pK of 3.1 was estimated for the acid ionization corresponding to the disruption of the two iron-protein bonds, and a pK of 8.1 was found for the weakly alkaline ionization accompanied by the disappearance of the 695 mµ absorption band. Comparison between these and the known analogous pK values for horse cytochrome c indicates that the closed crevice of the yeast protein is weaker to the extent of about 1 kcal per mole. The kinetics and equilibrium of the reaction of yeast iso-1-ferricytochrome c with cyanide were studied. The reaction shows the same characteristics as those found for the horse protein. The derived thermodynamic parameters for the association with CN− are ΔF = −7.6 kcal per mole, ΔH− =−12.9 kcal per mole, and ΔS = −17.8 e.u. The more favorable enthalpy and less favorable entropy changes than for the reaction with horse cytochrome c indicate that in the yeast protein the noncovalent interactions between various residues of the polypeptide chain are weaker and the molecule possesses more degrees of freedom.