title: Partial inactivation of cytochrome c oxidase by nonpolar mercurial reagents.
abstract: Purified beef heart cytochrome c oxidase is inactivated to the extent of 35 to 50% by the nonpolar mercurial reagents mercuric chloride and ethylmercuric chloride. The inactivation is complete within 5 min. In titrations of activity, the plateau level of inactivation is attained at added ethylmercuric chloride:heme a ratios of about 1:1. Up to 3 mercury atoms/heme a are bound to the oxidase, although only the first of these affects its enzymatic activity. Incubation of the ethylmercury-modified oxidase with sulfhydryl compounds reverses the inactivation, with 2,3-dimercaptopropanol being most effective of the reagents tested. Spectrophotometric and polarographic assays of enzymatic activity show that Km values for the native and the ethylmercury-modified enzymes are practically indistinguishable, and that the partial inactivation observed for the latter is reflected exclusively in a lower value of Vmax compared to that of the native enzyme. Based on these results, we propose that ethylmercuric chloride reacts with a single crucial--SH group per heme a, and that electron transfer processes in the modified product are partially inhibited.
mesh_terms: D000818:Animals; D002417:Cattle; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors*; D005034:Ethylmercuric Chloride / Q000494:pharmacology*; D005035:Ethylmercury Compounds / Q000494:pharmacology*; D007700:Kinetics; D008628:Mercury / Q000494:pharmacology*; D009206:Myocardium / Q000201:enzymology; D009994:Osmolar Concentration; D011048:Polarography; D011485:Protein Binding
chemical_list: D005035:Ethylmercury Compounds; D003576:Electron Transport Complex IV; D008628:Mercury; D005034:Ethylmercuric Chloride