Isolation and sequencing of the cDNA of a novel cytochrome P450 from rat oesophagus.

RT-PCR was used to find whether cytochromes P450 of the 2A, 2B and 2E sub-families are expressed in the rat oesophagus. This showed that this tissue expresses a previously unknown member of the CYP2B sub-family, now designated CYP2B21. Using a combination of 5'- and 3'-RACE (rapid amplification of cDNA ends) and library screening, the cDNA was amplified and sequenced. The cDNA sequence (GenBank accession no. AF159245) covers the whole of the coding region and the whole of the 3'-untranslated region (UTR), but only 17 nt of the 5'-UTR. The DNA sequence has strong similarity to those of CYP2B1 and CYP2B2, with the derived amino acid sequence being 84 and 83% identical, respectively. The ease with which this cDNA was found in the cDNA library suggests that CYP2B21 is a major P450 of the oesophagus. The catalytic activity of this new CYP2B is not yet known, but as previous authors have reported that other members of this sub-family (CYP2B1 or 2B2) metabolize the selective oesophageal carcinogen N:-nitrosomethylbutylamine with the chemical selectivity necessary for carcinogenesis, i.e. they preferentially hydroxylate the alpha-carbon of the butyl chain, this new CYP2B may be the nitrosamine-activating enzyme of the oesophagus.