1/10/2024 0 Comments ION M.G Chess free![]() ![]() The inhibition is specific for Ca 2+ and is reversed by EGTA. No inhibitory effect of Ca 2+ is observed under conventional conditions of cytochrome c oxidase activity assays (turnover number >100 s −1 at pH 8), which may explain why the effect was not noticed earlier. The inhibition is observed only at low, but physiologically relevant, turnover rates of the enzyme (∼10 s −1 or less). ![]() Here we report that Ca 2+ inhibits cytochrome oxidase activity of isolated bovine heart enzyme by 50–60% with K i of ∼1 µM, close to K d of calcium binding with the oxidase determined spectrophotometrically. However, no effect of Ca 2+ on the functional characteristics of cytochrome oxidase was revealed earlier. Ca 2+ shifts the absorption spectrum of heme a, which allowed previously to determine the kinetics and equilibrium characteristics of the binding. Cytochrome c oxidase from bovine heart binds Ca 2+ reversibly at a specific Cation Binding Site located near the outer face of the mitochondrial membrane. ![]()
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