title: Potentiometric study of cytochrome c1aa3 from Thermus thermophilus.
abstract: We have examined the redox behavior of the cytochrome c1aa3 complex from Thermus thermophilus. In potentiometric titrations the cytochrome c behaves as an independent center having n = 1 and E = 205 mV (NHE). Under the assumption that the individual centers equilibrate independently in this experiment, changes in the absorption band at 603 nm have been resolved into two components: cytochrome a (n = 1, Em = 270 mV, 60% spectral contribution) and cytochrome a3 (n = 2, Em = 360 mV, 40% spectral contribution). The n = 2 process was attributed to strong chemical coupling between cytochrome a3 and CuB. The enzyme was also titrated with a mixture of NADH and PMS, and the results are shown not to conform to a model of intramolecular equilibrium according to the equilibrium constants obtained from the potentiometric titration. It is suggested that a conformational equilibrium within the complex may control electron transfer between cytochromes a and a3.
authors.forename: T
authors.initials: T
authors.lastname: Yoshida
authors.forename: J A
authors.initials: JA
authors.lastname: Fee
mesh_terms: D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV; D008773:Methylphenazonium Methosulfate; D009243:NAD; D010084:Oxidation-Reduction; D011199:Potentiometry; D013053:Spectrophotometry; D013824:Thermus / Q000201:enzymology*
chemical_list: D009243:NAD; D008773:Methylphenazonium Methosulfate; D003576:Electron Transport Complex IV