Characterization of rat and human CYP2J enzymes as Vitamin D 25-hydroxylases

vitamin D is 25-hydroxylated in the liver, before being activated by 1α-hydroxylation in the kidney. Recently, the rat cytochrome P450 2J3 (CYP2J3) has been identified as a principal vitamin D 25-hydroxylase in the rat [Yamasaki T, Izumi S, Ide H, Ohyama Y. Identification of a novel rat microsomal vitamin D₃ 25-hydroxylase. J Biol Chem 2004;279(22):22848-56]. In this study, we examine whether human CYP2J2 that exhibits 73% amino acid homology to rat CYP2J3 has similar catalytic properties. Recombinant human CYP2J2 was overexpressed in Escherichia coli, purified, and assayed for vitamin D 25-hydroxylation activity. We found significant 25-hydroxylation activity toward vitamin D₃ (turnover number, 0.087 min^-1), vitamin D₂ (0.16 min^-1), and 1α-hydroxyvitamin D₃ (2.2 min^-1). Interestingly, human CYP2J2 hydroxylated vitamin D₂, an exogenous vitamin D, at a higher rate than it did vitamin D₃, an endogenous vitamin D, whereas, rat CYP2J3 hydroxylated vitamin D₃ (1.4 min^-1) more efficiently than vitamin D₂ (0.86 min^-1). Our study demonstrated that human CYP2J2 exhibits 25-hydroxylation activity as well as rat CYP2J3, although the activity of human CYP2J2 is weaker than rat CYP2J3. CYP2J2 and CYP2J3 exhibit distinct preferences toward vitamin D₃ and D₂.