Cytochrome P450-Dependent Monooxygenase: An Overview
In early studies on liver microsomes it was noticed that the heme content, measured by the pyridine hemochrome method, yielded values about double that of the content of the only known microsomal hemoprotein, cytochrome b5 (1). Reduction of the microsomes with sodium dithionite yielded, in the presence of carbon monoxide a “carbon monoxide-binding pigment” which was rationalized as not to be a hemoprotein (1, 2). The reasons cited for the CO-binding pigment not to be a hemoprotein included a) the absence of a reduced minus oxidized difference spectrum in the Soret region, b) lack of α- and β-peaks for the reduced, C0-complex, c) displacement of the CO-reduced absorption peak much further to the red than other carbon monoxy-hemoproteins, and d) the CO-complex showed no photodissociation. P450 was coined as a tentative name for the CO-complex, which was first reported to be hemoprotein in nature, in 1962 (3). Within the next few years cytochrome P450 was demonstrated to be the terminal oxidase in a number of microsomal monooxygenation reactions (4, 5).
KeywordsLiver Microsome P450 Reductase Cytochrome P450 Isozyme Hydroxy Amino Acid Liver Microsomal Cytochrome
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