title: An anlysis of the optical titrations of the 430 and 455 NM chromophores of ethyl isocyanide complexes of mammalian hepatic cytochrome P-450.
abstract: A computational method is presented from which one may calculate the pK for the spectral changes of the 430 and 455 mm chromophores of ethyl isocyanide complexes of rabbit and rat liver microsomal cytochrome P-450. For the rat liver protein from control or phenobarital-treated animals, the pK for the loss of the 430 nm absorption is approximately equal to the pK for the gain of the 455 nm absorption, confirming that the two chromophores are in pH equilibrium with one another. For a soluble preparation in which the chromophores exhibit the pH equilbrium property, this equilbrium is also maintained even after the addition of ethyl isocyanide. It is concluded that the appearance of a 430 nm absorption after the addition ethyl isocyanide to reduced cytochrome P-450 does not necessarily represent conversion of the protein to cytochrome P-420.
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004980:Ethane / Q000031:analogs & derivatives / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008433:Mathematics; D008862:Microsomes, Liver / Q000201:enzymology*; D008962:Models, Theoretical; D009570:Nitriles / Q000378:metabolism* / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D013057:Spectrum Analysis
chemical_list: D009570:Nitriles; C001187:ethyl isocyanide; D003577:Cytochrome P-450 Enzyme System; D004980:Ethane