Isolation and heterologous expression of cloned cDNAs for two rabbit nasal microsomal proteins, CYP2A10 and CYP2A11, that are related to nasal microsomal cytochrome P450 form a.

Nasal microsomal P450 form a (NMa), a major cytochrome P450 isozyme in rabbit olfactory and respiratory nasal mucosa with high activity toward a variety of odorants and environmental toxicants, was previously purified to electrophoretic homogeneity from rabbit nasal microsomes. In the present study, a cDNA library constructed from poly(A)+ RNA from rabbit respiratory nasal mucosa was screened with antibodies to P450 NMa, and five immunopositive clones were isolated and characterized. Sequence analysis indicated that the clones encode two highly similar P450s that contain 494 amino acid residues, with the first 20 corresponding to P450 NMa, and differ from each other in only 8 residues scattered throughout the polypeptide chains. On the basis of structural homology the two proteins are designated as CYP2A10 and CYP2A11 and are the first members of the P450 2A subfamily to be identified in nasal tissue. Genomic blot analysis indicated that 2A10 and 2A11 are apparently not allelic variants. Both genes are expressed in liver and lung as well as in nasal tissues, as judged by RNA blot analysis, but the relative levels of the two mRNAs differ. Both enzymes were partially purified after expression of the cDNAs in Escherichia coli and shown to catalyze the oxygenation of a variety of substrates, including ethanol and procarcinogens such as N-nitrosodiethylamine and phenacetin. P450 2A10 is generally more active than P450 2A11 and strikingly so in the conversion of testosterone to androstenedione.