Inter-relatedness of some isoenzymes of cytochrome P-450 from rat, rabbit and human, determined with monoclonal antibodies.

Monoclonal antibodies have been raised to rat liver cytochromes P-450 b and c, and rabbit liver cytochrome P-450 form 4. A total of six antibodies have been studied. Each antibody reacted strongly both with its homologous antigen and with microsomal fractions selectively enriched with that antigen by treatment of animals with inducing compounds. However, several of the antibodies showed cross-reactivity, either within or between species. A combination of enzyme-linked immunosorbent assay, immunoadsorption, Western blotting and competitive radioimmunoassay revealed that each of the antibodies reacted with a different epitope. Proteolytic digestion of antigen followed by Western blotting of the peptide fragments enabled antibodies, otherwise identical in their reactivity, to be distinguished. It is concluded that complex structural relationships exist amongst the different isoenzymes of cytochrome P-450 and that epitope mapping will help in characterizing both animal and human cytochromes P-450.