A new cytochrome P450 form belonging to the CYP2D in dog liver microsomes: purification, cDNA cloning, and enzyme characterization.

A new form of cytochrome P450 (P450 DUT2) was purified from untreated male dog liver microsomes. The final preparation (a specific content of 19.1 nmol P450/mg protein) showed a single band with an apparent monomeric molecular weight of 50,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but was further separated into two apoproteins (P450 DUT2a and P450 DUT2b) by reverse-phase HPLC. Both proteins had identical NH2-terminal amino acid sequences, but the first three amino acids of P450 DUT2b were truncated in P450 DUT2a. Purified P450 DUT2 showed 5 to 18 times higher catalytic activities than did hepatic microsomes toward desipramine, metoprolol, and dextromethorphan. These activities in dog liver microsomes were strongly inhibited by anti-P450 DUT2-IgG. A 1.7-kilobase pair cDNA (cDUT2) encoding a male dog liver P450 of 500 amino acid residues (molecular weight 56,400) was isolated and sequenced. The first 35 NH2-terminal amino acid sequence of P450 DUT2b coincided with the deduced amino acid sequence of cDUT2 at 2-36. The deduced total amino acid sequence of cDUT2 shared high similarity with the reported 2D forms (with 2D6, 74.6%; 2D14, 75.4%; 2D1, 65.4%; and 2D9, 63.6%). Moreover, the expressed P450 DUT2 in COS-7 cells had catalytic activities similar to those of purified P450 DUT2. Therefore, this paper is the first report about dog CYP2D. Furthermore, Northern and Western blot analyses indicated that the expressed levels of mRNA and protein were almost equal between male and female dogs. Western blot analysis suggested that P450 DUT2 is a constitutive and major (approximately 20% of the total P450) form, indicating that the 2D subfamily P450 in dog liver is quite unique from CYP2D members of other species.