Metabolism of vitamin D by human microsomal CYP2R1 |
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Authors: | Shinkyo Raku Sakaki Toshiyuki Kamakura Masaki Ohta Miho Inouye Kuniyo |
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Affiliation: | Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan. |
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Abstract: | The activation of vitamin D requires 25-hydroxylation in the liver and 1alpha-hydroxylation in the kidney. However, it remains unclear which enzyme is relevant to vitamin D 25-hydroxylation. Recently, human CYP2R1 has been reported to be a potential candidate for a hepatic vitamin D 25-hydroxylase. Thus, vitamin D metabolism by CYP2R1 was compared with human mitochondrial CYP27A1, which used to be considered a physiologically important vitamin D(3) 25-hydroxylase. A clear difference was observed between CYP2R1 and CYP27A1 in the metabolism of vitamin D(2). CYP2R1 hydroxylated vitamin D(2) at the C-25 position while CYP27A1 hydroxylated it at positions C-24 and C-27. The K(m) and k(cat) values for the CYP2R1-dependent 25-hydroxylation activity toward vitamin D(3) were 0.45microM and 0.97min(-1), respectively. The k(cat)/K(m) value of CYP2R1 was 26-fold higher than that of CYP27A1. These results strongly suggest that CYP2R1 plays a physiologically important role in the vitamin D 25-hydroxylation in humans. |
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Keywords: | Cytochrome P450 CYP2R1 Vitamin D metabolism Vitamin D 25-hydroxylation |
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