Metabolism of vitamin D(3) by human CYP27A1.
Human vitamin D(3) 25-hydroxylase (CYP27A1) cDNA was expressed in Escherichia coli, and its enzymatic properties were revealed. The reconstituted system containing the membrane fraction prepared from the recombinant E. coli cells was examined for the metabolism of vitamin D(3). Surprisingly, at least eight forms of metabolites including the major product 25(OH)D(3) were observed. HPLC analysis and mass spectrometric analysis suggested that those metabolites were 25(OH)D(3), 26(OH)D(3), 27(OH)D(3), 24R,25(OH)(2)D(3), 1alpha, 25(OH)(2)D(3, )25,26(OH)(2)D(3) (25,27(OH)(2)D(3)), 27-oxo-D(3) and a dehydrogenated form of vitamin D(3). These results suggest that human CYP27A1 catalyzes multiple reactions and multiple-step metabolism toward vitamin D(3). The K(m) and V(max) values for vitamin D(3) 25-hydroxylation and 25(OH)D(3) 1alpha-hydroxylation were estimated to be 3.2 microM and 0.27 (mol/min/mol P450), and 3.5 microM and 0.021 (mol/min/mol P450), respectively. These kinetic studies have made it possible to evaluate a physiological meaning of each reaction catalyzed by CYP27A1.
Sawada
N
N
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan.
Sakaki
T
T
Ohta
M
M
Inouye
K
K
D001483:Base Sequence; D002384:Catalysis; D002762:Cholecalciferol / Q000378:metabolism*; D053493:Cholestanetriol 26-Monooxygenase; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D018076:DNA, Complementary; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D013058:Mass Spectrometry; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; D018076:DNA, Complementary; D011994:Recombinant Proteins; D002762:Cholecalciferol; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase