HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Blair, D. F. Articles by Chan, S. I. Search for Related Content PubMed PubMed Citation Articles by Blair, D. F. Articles by Chan, S. I. Social Bookmarking                      What's this?

J. Biol. Chem., Vol. 261, Issue 25, 11524-11537, Sep, 1986

Spectroelectrochemical study of cytochrome c oxidase: pH and temperature dependences of the cytochrome potentials. Characterization of site-site interactions

DF Blair, WR Ellis Jr, H Wang, HB Gray and SI Chan

The cytochrome a and a3 sites in uninhibited, detergent-solubilized cytochrome c oxidase have been studied under a wide range of conditions using thin-layer spectroelectrochemistry. The observed absorbance changes at the alpha and Soret absorbance maxima have been used together to estimate the extents of reduction of cytochromes a and a3, using the absorbance properties of these cytochromes deduced from previous measurements employing ligand inhibition of cytochrome a3. The resulting Nernst plots, combined with the results of parallel studies on the carbon monoxide-inhibited enzyme (Ellis, W. R., Jr., Wang, H., Blair, D. F., Gray, H. B., and Chan, S. I. (1986) Biochemistry 25, 161- 167; Wang, H., Blair, D. F., Ellis, W. R., Jr., Gray, H. B., and Chan, S. I. (1986) Biochemistry 25, 167-171), indicate that the cytochrome a site participates in anticooperative thermodynamic interactions which involve all three of the other metal sites in the protein. Using an analysis which resolves the intrinsic thermodynamic properties of the cytochromes from the effects of the intersite interactions, the pH, temperature, and ionic strength dependences of the cytochrome reduction potentials have been measured. The standard entropy of reduction of cytochrome a in the native enzyme is large and negative, in agreement with measurements on the carbon monoxide-inhibited enzyme. The reduction potential of cytochrome a is only moderately (less than -30 mV/pH unit) dependent upon pH, which implies that its reduction is linked to the uptake, on the average, of only about 0.5 protons at pH 7.0, and significantly less at the higher pH values relevant to the mitochondrial matrix. The thermodynamic properties of cytochrome a3 were found to be different in the two enzyme batches studied: in one batch, the cytochrome a3 reduction potential decreased steeply (about - 56 mV/pH unit) with increasing pH, indicating stoichiometric (1 H+/e-) coupling of protonation to reduction. In the other batch, the cytochrome a3 potential was insensitive to pH below pH 7.5 and decreased at higher pH values in a manner suggesting coupling to an ionizable group with pKa near 7.8. The temperature dependence of the cytochrome a3 reduction potential indicates that its standard entropy of reduction is more positive than that of myoglobin, another high-spin metalloprotein heme, and significantly more positive than that of cytochrome a.(ABSTRACT TRUNCATED AT 400 WORDS)
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				A. F. Verissimo, F. L. Sousa, A. M. Baptista, M. Teixeira, and M. M. Pereira Thermodynamic Redox Behavior of the Heme Centers in A-Type Heme-Copper Oxygen Reductases: Comparison between the Two Subfamilies Biophys. J., November 1, 2008; 95(9): 4448 - 4455. [Abstract] [Full Text] [PDF]

				I. Belevich, D. A. Bloch, N. Belevich, M. Wikstrom, and M. I. Verkhovsky Exploring the proton pump mechanism of cytochrome c oxidase in real time PNAS, February 20, 2007; 104(8): 2685 - 2690. [Abstract] [Full Text] [PDF]

				H. J. Hwang and Y. Lu pH-dependent transition between delocalized and trapped valence states of a CuA center and its possible role in proton-coupled electron transfer PNAS, August 31, 2004; 101(35): 12842 - 12847. [Abstract] [Full Text] [PDF]

				M. Mochizuki, H. Aoyama, K. Shinzawa-Itoh, T. Usui, T. Tsukihara, and S. Yoshikawa Quantitative Reevaluation of the Redox Active Sites of Crystalline Bovine Heart Cytochrome c Oxidase J. Biol. Chem., November 19, 1999; 274(47): 33403 - 33411. [Abstract] [Full Text] [PDF]

				R. B. Gennis How does cytochrome oxidase pump protons? PNAS, October 27, 1998; 95(22): 12747 - 12749. [Full Text] [PDF]

				B. E. Schultz and S. I. Chan Thermodynamics of electron transfer in Escherichia coli cytochrome bo3 PNAS, September 29, 1998; 95(20): 11643 - 11648. [Abstract] [Full Text] [PDF]

				M. Brunori, A. Giuffre, E. D'Itri, and P. Sarti Internal Electron Transfer in Cu-Heme Oxidases. THERMODYNAMIC OR KINETIC CONTROL? J. Biol. Chem., August 8, 1997; 272(32): 19870 - 19874. [Abstract] [Full Text] [PDF]

				P. Brzezinski and M. T. Wilson Photochemical electron injection into redox-active proteins PNAS, June 10, 1997; 94(12): 6176 - 6179. [Abstract] [Full Text] [PDF]