Protons,pumps, and potentials: Control of cytochrome oxidase |
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Authors: | Peter Nicholls Peter Butko |
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Institution: | (1) Department of Biological Sciences, Brock University, L2S 3A1 St. Catharines, Ontario, Canada;(2) Present address: National Research Council, Institute for Biological Sciences, K1A 0R6 Ottawa, Ontario, Canada |
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Abstract: | Cytochromec oxidase oxidizes cytochromec and reduces molecular oxygen to water. When the enzyme is embedded across a membrane, this process generates electrical and pH gradients, and these gradients inhibit enzyme turnover. This respiratory control process is seen both in intact mitochondria and in reconstituted proteoliposomes. Generation of pH gradients and their role in respiratory control are described. Both electron and proton movement seem to be implicated. A topochemical arrangement of redox centers, like that in the photosynthetic reaction center and the cytochromebc
1 complex, ensures charge separation as a result of electron movement. Proton translocation does not require such a topology, although it does require alternating access to the two sides of the membrane by proton-donating and accepting groups. The sites of respiratory control within the enzyme are discussed and a model presented for electron transfer and proton pumping by the oxidase in the light of current knowledge of the transmembranous location of the redox centers involved. |
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Keywords: | Cytochrome oxidase proteoliposome respiratory control membrane potential pH gradient cytochromec oxygen proton pump |
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