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The steady-state mechanism of cytochrome c oxidase: Redox interactions between metal centres

Mason, MG and Nicholls, P and Cooper, CE (2009) 'The steady-state mechanism of cytochrome c oxidase: Redox interactions between metal centres.' Biochemical Journal, 422 (2). 237 - 246. ISSN 0264-6021

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Abstract

The steady-state behaviour of isolated mammalian cytochrome c oxidase was examined by increasing the rate of reduction of cytochrome c. Under these conditions the enzyme's 605 (haern a), 655 (haem a /CU ) and 830 (Cu ) nm spectral features behaved as if they were at near equilibrium with cytochrome c (550 nm). This has implications for non-invasive tissue measurements using visible (550, 605 and 655 nm) and near-IR (830 nm) light. The oxidized species represented by the 655 nm band is bleached by the presence of oxygen intermediates P and F (where P is characterized by an absorbance spectrum at 607 nm relative to the oxidized enzyme and F is characterized by an absorbance spectrum at 580 nm relative to the oxidized enzyme) or by reduction of haem a or CU . However, at these ambient oxygen levels (far above the enzyme K ), the populations of reduced haem a and the oxygen intermediates were very low (<10%). We therefore interpret 655 nm changes as reduction of the otherwise spectrally invisible CU centre. We present a model where small anti-cooperative redox interactions occur between haem a-CU - CU (steady-state potential ranges: CU , 212-258 mV; haem a, 254-281 mV, CU , 227-272 mV). Contrary to static equilibrium measurements, in the catalytic steady state there are no high potential redox centres; (>300 mV). We find that the overall reaction is correctly described by the classical model in which the Michaelis intermediate is a ferrocytochrome c-enzyme complex. However, the oxidation of ferrocytochrome c in this complex is not the sole rate-determining step. Turnover is instead dependent upon electron transfer from haem a to haem a , but the haem a potential closely matches cytochrome c at all times. © The Authors Journal compilation. © 2009 Biochemical Society. 3 B A 3 B m 3 B A B A B 3

Item Type: Article
Subjects: Q Science > QH Natural history > QH301 Biology
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Jim Jamieson
Date Deposited: 16 Sep 2011 09:02
Last Modified: 30 Mar 2021 20:15
URI: http://repository.essex.ac.uk/id/eprint/655

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