Immunochemical identification of cytochrome P-450 isozyme 3a (P-450ALC) in rabbit nasal and kidney microsomes and evidence for differential induction by alcohol.

Polyclonal and monoclonal antibodies to rabbit liver microsomal alcohol-inducible cytochrome P-450 isozyme 3a (P-450ALC) were used to examine the tissue distribution of the cytochrome. Isozyme 3a or an immunochemically indistinguishable variant of this protein was detected on immunoblots of kidney and nasal mucosa microsomes, but not of microsomes prepared from brain, lung, adrenal, heart, intestine, ovary, spleen, testis, or uterus from untreated or ethanol-treated rabbits. The presence of isozyme 3a was also indicated by inhibition by anti-3a IgG of microsomal aniline hydroxylation and butanol oxidation. The identity of isozyme 3a was further substantiated by peptide-mapping analysis of the immunoaffinity-purified proteins. The amount of isozyme 3a was increased in kidney, but not in nasal microsomes, by chronic ethanol treatment. The induction of isozyme 3a in the kidney was reflected in a more than 2-fold increase in the total rates and a 7-fold increase in the isozyme 3a-dependent rates of aniline and butanol metabolism. Based on immunoblot quantitation, the specific content of isozyme 3a is about 10 pmol/mg of protein in kidney and 80 pmol/mg of protein in nasal microsomes of untreated rabbits. After ethanol treatment of the animals, the content increases to 50 pmol/mg of protein in kidney but is unchanged in nasal microsomes. The presence of isozyme 3a may play a significant role in the toxicity of foreign compounds.