Efect of calcium ions on electron transfer between hemes a and a3 in cytochrome-c oxidaseстатья
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Дата последнего поиска статьи во внешних источниках: 27 декабря 2018 г.
Аннотация:Kinetics of the reduction of the hemes in cytochrome c oxidase in the presence of high concentration of ruthenium(III)hexaammine chloride was examined using a stopped-flow spectrophotometer. Upon mixing of the oxidized enzyme with dithionite and Ru(NH3)63+ , three well-resolved phases were observed: heme a reduction reaching completion within few milliseconds is followed by two slow phases of heme a3 reduction. The difference spectrum of heme a3 reduction in the visible region is characterized by a maximum at ~612 nm rather than at 603 nm as believed earlier. It is shown that in the case of bovine heart cytochrome c oxidase containing a special cation-binding center in which reversible binding of calcium ion occurs, heme a3 reduction is slowed down by low concentrations of Ca2+. The effect is absent in case of the bacterial cytochrome oxidase in which the cation-binding center contains a tightly bound Ca2+ ion. The data obtained corroborate the inhibition of the cytochrome oxidase enzymatic activity by Ca2+ ions discovered earlier and indicates that the cation affects intramolecular electron transfer.