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BIOLOGICAL SCIENCES / PHARMACOLOGY
Genetics of P450 oxidoreductase: Sequence variation in 842 individuals of four ethnicities and activities of 15 missense mutations

Ningwu Huang^*, Vishal Agrawal^*, Kathleen M. Giacomini, and Walter L. Miller^*,

Departments of *Pediatrics and Biopharmaceutical Sciences, University of California, San Francisco, CA 94143

Communicated by Melvin M. Grumbach, University of California School of Medicine, San Francisco, CA, December 11, 2007 (received for review November 1, 2007)

P450 oxidoreductase (POR) is an electron-donating flavoprotein required for the activity of all microsomal cytochrome P450 enzymes. We sequenced 5,655 bp of the POR gene in a representative population of 842 healthy unrelated individuals in four ethnic groups: 218 African Americans, 260 Caucasian Americans, 179 Chinese Americans, and 185 Mexican Americans. One hundred forty SNPs were detected, of which 43 were found in 1% of alleles. Twelve SNPs were in the POR promoter region. Fifteen of 32 exonic variations altered the POR amino acid sequence; 13 of these 15 are previously undescribed missense variations. We found eight indels, only one of which was in the coding region. A previously described variant, A503V, was found on 27.9% of all alleles with some ethnic predilection (19.1% in African Americans, 26.4% in Caucasian Americans, 36.7% Chinese Americans, and 31.0% in Mexican Americans). We built cDNA expression vectors for the 13 previously undescribed missense variants, expressed each protein lacking 27 N-terminal residues in Escherichia coli, and assayed the apparent K_m and V_max of each in four assays: reduction of cytochrome c, oxidation of NADPH, 17-hydroxylase activity of P450c17, and 17,20 lyase activity of P450c17. The catalytic activities of several missense mutants differed substantially in these assays, indicating that each POR mutant must be assayed separately with each potential target P450 enzyme. The activity of A503V was reduced to a modest but statistically significant degree in all four assays, suggesting that it may play an important role in interindividual variation in drug response.

cytochrome P450 | drug metabolism | electron transfer | pharmacogenomics | steroidogenesis

The authors declare no conflict of interest.

This article contains supporting information online at www.pnas.org/cgi/content/full/0711621105/DC1.

To whom correspondence should be addressed at: Department of Pediatrics, HSE 1401, 513 Parnassus Avenue, University of California, San Francisco, CA 94143-0978. E-mail: wlmlab{at}ucsf.edu

© 2008 by The National Academy of Sciences of the USA

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