Tissue- and species-dependent expression of multiple forms of mammalian microsomal flavin-containing monooxygenase.

The immunochemical relatedness, multiplicity, and expression of microsomal flavin-containing monooxygenases were assessed in hepatic, pulmonary, and renal microsomal preparations from adult, male rabbits, mice, rats, guinea pigs, and hamsters. Preparations from adult female (pregnant and nonpregnant) and immature male and female rabbits were also examined. Microsomes were analyzed by immunoblotting with polyclonal antibodies to flavin-containing monooxygenases purified from pig, mouse, and rabbit liver, and rabbit lung. Pulmonary flavin-containing monooxygenases, which differ from the major forms of the enzyme present in liver, were detected in pulmonary samples from all species. The major hepatic enzymes, or very closely related proteins, were also detected in pulmonary samples from every species except the rabbit. Three forms of pulmonary flavin-containing monooxygenase are found in rabbit and guinea pig. Differences in the expression of these three forms were observed with rabbits; all three were detected with some individuals and only two with others. The hepatic form of the flavin-containing monooxygenase is present in kidney of all species examined, and the pulmonary form is detected in kidney of rabbits, mice, and hamsters, but not rats or guinea pigs. Kidneys and lungs of individual rabbits were of the same phenotype with respect to the expression of the pulmonary forms of the enzyme. The findings show that the expression of flavin monooxygenase isozymes is tissue and species dependent.