The isolation and characterisation of human cytochromes P-450
The metabolism of drugs and foreign compounds is a major influence on their pharmacological and toxicological effects. The haemoprotein cyt. P-450 exists as a multi-isozyme family which functions in the metabolism of a wide variety of foreign compounds. Biochemical information concerning the structure and catalytic function of cyt. P-450 isozymes from man is less extensive than from animal species. In this study several microsomal proteins including four cyt. P-450 isozymes, NADPH-cyt. P-450 reductase, epoxide hydrolase and other unidentified proteins were purified from adult human liver; the methodologies previously employed to isolate cyt. P-450 isozymes were improved and now allow better resolution and recovery of human cyt. P-450. Comparison of the physical and chromatographic properties of the cyt. P-450 isozymes isolated (cyt. P-450 7:3 cyt. P-4507:4 and cyt. P-4507:5) indicated that they were very similar and probably identical. N-terminal amino acid sequence and immunochemical data demonstrated that these isozymes probably belong to the steroid-inducible gene family. Further characterisation of cyt. P-4507:3 indicated that it is a major inducible isozyme in man and that it metabolises the calcium entry blocker nifedipine but not a structurally similar drug nicardipine.