Peculiarities of cyanide binding to the [ba.sub.3]-type cytochrome oxidase from the thermophilic bacterium Thermus thermophilus

Cytochrome c oxidase of the [ba.sub.3]-type from Thermus thermophilus does not interact with cyanide in the oxidized state and acquires the ability to bind heme iron ligands only upon reduction. Cyanide complexes of the reduced heme [a.sub.3] in cytochrome [ba.sub.3] and in mitochondrial [aa.sub.3]-...

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Bibliographic Details
Published in:Biochemistry (Moscow) 2010-03, Vol.75 (3), p.342
Main Authors: Kalinovich, A.V, Azarkina, N.V, Vygodina, T.V, Soulimane, T, Konstantinov, A.A
Format: Article
Language:English
Subjects:
Bacteria
Chemical properties
Cyanides
Cytochrome c
Cytochrome oxidase
Heme
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Summary:Cytochrome c oxidase of the [ba.sub.3]-type from Thermus thermophilus does not interact with cyanide in the oxidized state and acquires the ability to bind heme iron ligands only upon reduction. Cyanide complexes of the reduced heme [a.sub.3] in cytochrome [ba.sub.3] and in mitochondrial [aa.sub.3]-type cytochrome oxidase are similar spectroscopically, but the [a.sup.2+.sub.3]--CN complex of cytochrome [ba.sub.3] is strikingly tight. Experiments have shown that the [K.sub.d] value of the cytochrome [ba.sub.3] complex with cyanide in the presence of reductants of the enzyme binuclear center does not exceed [10.sup.-8] M, which is four to five orders of magnitude less than the [K.sub.d] of the cyanide complex of the reduced heme [a.sub.3] of mitochondrial cytochrome oxidase. The tightness of the cytochrome [ba.sub.3] complex with cyanide is mainly associated with an extremely slow rate of the ligand dissociation ([k.sub.off] ≤ [10.sup.-7] [sec.sup.-1]), while the rate of binding ([k.sub.on] ~ [10.sup.2] [M.sup.-1] x [sec.sup.-1]) is similar to the rate observed for the mitochondrial cytochrome oxidase. It is proposed that cyanide dissociation from the cytochrome [ba.sub.3] binuclear center might be hindered sterically by the presence of the second ligand molecule in the coordination sphere of [Cu.sup.2+.sub.B]. The rate of cyanide binding with the reduced heme [a.sub.3] does not depend on pH in the neutral area, but it approaches linear dependence on [H.sup.+] activity in the alkaline region. Cyanide binding appears to be controlled by protonation of an enzyme group with p[K.sub.a] = 8.75. DOI: 10.1134/S0006297910030119 Key words: cytochrome oxidase [ba.sub.3], cyanide, hemoproteins, oxygen reducing center, Thermus thermophilus
ISSN:0006-2979
DOI:10.1134/S0006297910030119