Pharmacogenetics of P450 oxidoreductase: effect of sequence variants on activities of CYP1A2 and CYP2C19.
OBJECTIVE
All microsomal cytochrome P450s enzymes, including those that metabolize the majority of clinically used drugs, require electron transfer through P450 oxidoreductase (POR). Mutations in human POR cause altered steroidogenesis and congenital malformations, but the clinical effects on drug metabolism are unclear. We examined the effects of POR sequence variants on two drug-metabolizing P450 enzymes, CYP1A2 and CYP2C19.


METHODS
Our previous sequencing of the human POR gene in POR-deficient patients and in 842 normal individuals identified 35 sequence variants. We expressed these 35 POR sequence variants in bacteria, reconstituted them with the CYP enzymes in vitro, and assayed their activities with human CYP1A2 and CYP2C19.


RESULTS
POR variants affected the activities of these enzymes to different extents. Disease-causing POR mutations A287P and R457H diminished catalysis by CYP1A2 and CYP2C19 to barely detectable levels. POR A503V, a polymorphism found in 28% of alleles in the normal population, had 85% of wild-type activity with CYP1A2 and 113% of wild-type activity with CYP2C19. Q153R, a disease-causing mutation that severely impaired steroidogenic activity and cytochrome c reduction, increased the activity of CYP1A2 to 144% and CYP2C19 activity to 284% of control.


CONCLUSIONS
The activity of individual POR mutants may vary greatly depending on the electron recipient used to assay activity. Thus, the activity of a POR mutant to support catalysis by a particular P450 enzyme cannot be predicted by the activity of that POR mutant in an assay with a different P450 or with cytochrome c.
Department of Pediatrics, University of California, San Francisco, California 94143-0978, USA.
Vishal
V
Agrawal
Ningwu
N
Huang
Walter L
WL
Miller
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D002384:Catalysis; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism*; D065731:Cytochrome P-450 CYP2C19; D004789:Enzyme Activation / Q000235:genetics; D004926:Escherichia coli; D006801:Humans; D008658:Inactivation, Metabolic / Q000235:genetics; D007700:Kinetics; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000235:genetics* / Q000378:metabolism; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D051381:Rats; D013379:Substrate Specificity / Q000235:genetics; D014169:Transformation, Bacterial
D050505:Mutant Proteins; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C045793:CYP2C19 protein, human; D019388:Cytochrome P-450 CYP1A2; D065731:Cytochrome P-450 CYP2C19; D009251:NADPH-Ferrihemoprotein Reductase