Evidence of the existence of structurally distinct hepatic and pulmonary forms of microsomal flavin-containing monooxygenase in the rabbit.

The flavin-containing monooxygenase has been purified from rabbit liver and lung microsomes. SDS-PAGE analysis shows that both enzyme forms migrate as a single band with an apparent Mr of 59000. The NH2-terminus of both forms is blocked. The liver oxidase contains a lower percentage of glutamine/glutamate and a greater amount of phenylalanine than does the lung flavoprotein. Polyclonal antibodies to a 14-amino-acid peptide obtained after CNBr cleavage of the liver oxidase cross-react with the microsomal and purified liver enzyme, but do not recognize the lung oxidase. HPLC profiles of tryptic digests of the liver and lung enzymes exhibit different patterns. Sequence alignment of selected peptides from the liver and lung oxidases reveals aberrant residues within homologous segments. These findings are interpreted to mean that both enzymes represent distinct gene products.