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== Publication Abstract from PubMed ==

The crystal structure of bovine cytochrome c oxidase (CcO) shows a sodium ion (Na(+)) bound to the surface of subunit I. Changes in the absorption spectrum of heme a caused by calcium ions (Ca(2+)) are detected as small red shifts, and inhibition of enzymatic activity under low turnover conditions is observed by addition of Ca(2+) in a competitive manner with Na(+). In this study, we determined the crystal structure of Ca(2+)-bound bovine CcO in the oxidized and reduced states at 1.7 A resolution. Although Ca(2+) and Na(+) bound to the same site of oxidized and reduced CcO, they led to different coordination geometries. Replacement of Na(+) with Ca(2+) caused a small structural change in the loop segments near the heme a propionate and formyl groups, resulting in spectral changes in heme a. Redox-coupled structural changes observed in the Ca(2+)-bound form were the same as those previously observed in the Na(+)-bound form, suggesting that binding of Ca(2+) does not severely affect enzymatic function, which depends on these structural changes. The relation between the Ca(2+) binding and the inhibitory effect during slow turnover, as well as the possible role of bound Ca(2+) are discussed.

Calcium-bound structure of bovine cytochrome c oxidase.,Muramoto K, Shinzawa-Itoh K Biochim Biophys Acta Bioenerg. 2023 Jan 25;1864(2):148956. doi: , 10.1016/j.bbabio.2023.148956. PMID:36708913<ref>PMID:36708913</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

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== References ==

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