title: Conformations of cytochrome oxidase: thermodynamic evaluation of the interconversion of the 418- and 428-nm forms.
abstract: Oxidized cytochrome c oxidase exists in two reasonably well-defined conformations, a high-spin conformation with maximal absorption at 418 nm and a low-spin conformation with maximal absorption at 428 nm. The equilibrium between these two conformations has been studied as a function of pH, pressure, and temperature. pH effects the equilibrium between the two conformations, the maximum fraction of the 418-nm form being found at about pH 6.8. Increasing pressure displaced the equilibrium toward the 428-nm form; the molar volume changes found are independent of pH but strongly dependent on temperature. Increasing temperature over the range -20 to 25 degrees C displaces the equilibrium toward the 428-nm form; the van't Hoff plots that result show a discontinuity at about 10 degrees C. Above 10 degrees C, delta H is relatively constant as a function of pH; below 10 degrees C, delta H is strongly pH dependent. Delta G, delta H, delta S, and delta V have been evaluated for the equilibrium.
mesh_terms: D000818:Animals; D002417:Cattle; D003576:Electron Transport Complex IV; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D011312:Pressure; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D003576:Electron Transport Complex IV