A flash-photolysis study of the reactions of acaa 3-ttype cytochrome oxidase with dioxygen and carbon monoxide |
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Authors: | Shun Hirota Margareta Svensson-Ek Pia Ädelroth Nobuhito Sone Thomas Nilsson Bo G. Malmström Peter Brzezinski |
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Affiliation: | (1) Department of Biochemistry and Biophysics, Göteborg University, Medicinaregatan 9C, S-413 90 Göteborg, Sweden;(2) Department of Functional Molecular Science, The Graduate University for Advanced Studies, Myodaiji, 444 Okazaki, Japan;(3) Department of Biochemical Engineering and Science, Kyushu Institute of Technology, 680 Kawazu, Iizuka, 820 Fukuoka, Japan |
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Abstract: | The time course of absorbance changes following flash photolysis of the fully-reduced carboxycytochrome oxidase fromBacillus PS3 in the presence of O2 has been followed at 445, 550, 605, and 830 nm, and the results have been compared with the corresponding changes in bovine cytochrome oxidase. The PS3 enzyme has a covalently bound cytochromec subunit and the fully-reduced species therefore accommodates five electrons instead of four as in the bovine enzyme. In the bovine enzyme, following CO dissociation, four phases were observed with time constants of about 10 s, 30 s, 100 s, and 1 ms at 445 nm. The initial, 10- s absorbance change at 445 nm is similar in the two enzymes. The subsequent phases involving hemea and CuA are not seen in the PS3 enzyme at 445 nm, because these redox centers are re-reduced by the covalently bound cytochromec, as indicated by absorbance changes at 550 nm. A reaction scheme consistent with the experimental observations is presented. In addition, internal electron-transfer reactions in the absence of O2 were studied following flash-induced CO dissociation from the mixed-valence enzyme. Comparisons of the CO recombination rates in the mixed-valence and fully-reduced oxidases indicate that more electrons were transferred from hemea3 toa in PS3 oxidase compared to the bovine enzyme. |
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Keywords: | Oxygen intermediates electron transfer flow flash Bacillus PS3 |
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