Catalytic Assays for Human Cytochrome P450

Cytochrome P450 (P450) enzymes catalyze the blotransformatlon of a broad range of structurally diverse foreign chemicals and endogenous substances. Many P450 enzymes have been isolated and identified in liver and other tlssues, including kidney, lung, intestines, and brain. Although these enzymes have a high degree of similarity in their ammo-acid sequences, many of them are subject to differential regulation and have distinct catalytic functions With the development of P450 form-specific (or P450 subfamlly-specific) inhlbltory antibodies, the discovery of enzyme-selective chemical inhibitors, and the general availability of catalytically active, mdivldual P450 cDNA-expressed proteins, several substrates, including drugs and endogenous substances, have been identified as useful catalytic monitors for specific P450 enzymes or subfamilies (see Table 1 ). These catalytic monitors can serve as useful expenmental tools in a variety of studies. These include studies designed: 1 To identify individual P45Os that catalyze the actlvatlon or detoxification of a particular compound, 2 To quantify the expression and catalytic activity of an mdlvrdual P450 in tissue samples and In cultured cells, 3. To analyze the enzyme kinetics of a particular P450; and 4 To eluctdate the mechanism of interaction between xenoblotlcs and mdlvldual P450 enzymes