Conformational change of cytochrome a3 induced by oxidized cytochrome c

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Abstract
Cyanide binding with the oxidized resting Yonetani‐type cytochrome c‐oxidase followed spectrophotometrically reveals a relatively rapid initial phase the rate of which shows saturation behaviour with respect to [HCN] and secondary slower absorption changes to a first approximation independent of the ligand concentration. Oxidized cytochrome c greatly accelerates the initial phase of cyanide binding but does not affect significantly contribution or rate constant of the slow phase. The same effect is exerted by poly‐L‐lysine. Within a framework of a reaction mechanism assuming Cu2+ B to be the initial HCN‐binding site, cytochrome c 3+ and other polycations are likely to bring about a conformational change of cytochrome oxidase resulting in an increased affinity of Cu2+ B for HCN. This could occur by virtue of loosening a bond between Cu2+ B and one of its endogenous ligands facilitating displacement of the latter by HCN.