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      Sulfide inhibition of and metabolism by cytochrome c oxidase.

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          Abstract

          Hydrogen sulfide (H2S), a classic cytochrome c oxidase inhibitor, is also an in vitro oxidase substrate and an in vivo candidate hormonal ('gasotransmitter') species affecting sleep and hibernation. H2S, nitric oxide (NO) and carbon monoxide (CO) share some common features. All are low-molecular-mass physiological effectors and also oxidase inhibitors, capable of binding more than one enzyme site, and each is an oxidizable 'substrate'. The oxidase oxidizes CO to CO2, NO to nitrite and sulfide to probable persulfide species. Mitochondrial cytochrome c oxidase in an aerobic steady state with ascorbate and cytochrome c is rapidly inhibited by sulfide in a biphasic manner. At least two successive inhibited species are involved, probably partially reduced. The oxidized enzyme, in the absence of turnover, occurs in at least two forms: the 'pulsed' and 'resting' states. The pulsed form reacts aerobically with sulfide to form two intermediates, 'P' and 'F', otherwise involved in the reaction of oxygen with reduced enzyme. Sulfide can directly reduce the oxygen-reactive a3CuB binuclear centre in the pulsed state. The resting enzyme does not undergo such a step, but only a very slow one-electron reduction of the electron-transferring haem a. In final reactivation phases, both the steady-state inhibition of catalysis and the accumulation of P and F states are reversed by slow sulfide oxidation. A model for this complex reaction pattern is presented.

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          Author and article information

          Journal
          Biochem. Soc. Trans.
          Biochemical Society transactions
          1470-8752
          0300-5127
          Oct 2013
          : 41
          : 5
          Affiliations
          [1 ] *School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, U.K.
          Article
          BST20130070
          10.1042/BST20130070
          24059525
          059a803f-541d-48b6-a04f-aec747c7fa01

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