Porcine Microsomal Vitamin D3 25-Hydroxylase (CYP2D25)

• Published in: The Journal of biological chemistry 2000-11, Vol.275 (44), p.34650-34655
• Main Authors: Hosseinpour, Fardin, Wikvall, Kjell
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M004185200

The metabolic activation of the prohormone vitamin D3 requires a 25-hydroxylation that has been reported to be catalyzed by both mitochondrial CYP27A and a microsomal vitamin D3 25-hydroxylase in the liver. CYP27A has been extensively studied, but its role as a physiologically important vitamin D3 25-hydroxylase has been questioned. The present paper reports that the microsomal vitamin D325-hydroxylase, purified from pig liver, converted vitamin D3 into 25-hydroxyvitamin D3 in substrate concentrations which are within the physiological range (apparentKm = 0.1 μm). The enzyme 25-hydroxylated vitamin D3, 1α-hydroxyvitamin D3 and vitamin D2 and also converted tolterodine, a substrate for human CYP2D6, into its 5-hydroxymethyl metabolite. Tolterodine inhibited the microsomal 25-hydroxylation, whereas quinidine, an inhibitor of CYP2D6, did not markedly inhibit the reaction. The primary structure of the microsomal vitamin D3 25-hydroxylase, designated CYP2D25, shows 77% identity with that of human CYP2D6. Northern blot and reverse transcription-polymerase chain reaction experiments revealed that CYP2D25 mRNA is expressed in higher levels in liver than in kidney and in small amounts in adrenals, brain, heart, intestine, lung, muscle, spleen, and thymus. Experiments with human liver microsomes and recombinantly expressed CYP2D6 strongly indicate that the microsomal 25-hydroxylation of vitamin D3 in human liver is catalyzed by an enzyme different from CYP2D6.