The R144C change in the CYP2C9*2 allele alters interaction of the cytochrome P450 with NADPH:cytochrome P450 oxidoreductase.

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Crespi CL, Miller VP

The R144C change in the CYP2C9*2 allele alters interaction of the cytochrome P450 with NADPH:cytochrome P450 oxidoreductase.

Pharmacogenetics. 1997 Jun;7(3):203-10.

PubMed ID

9241660 [ View in PubMed

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Abstract

We have examined the kinetics of substrate metabolism by cDNA-expressed human CYP2C9 and the R144C variant. Both enzymes exhibited similar apparent K(m) values for (S)-warfarin 7-hydroxylation, diclofenac 4'-hydroxylation and lauric acid 11-hydroxylation. In contrast, the R144C variant (relative to CYP2C9) had slower rates of metabolism for all three substrates. The difference was most pronounced for (S)-warfarin. Surprisingly, the magnitude of the difference was found to be dependent on the cytochrome P450 to NADPH-cytochrome P450 reductase (OR) ratio in the system (the difference being more pronounced at higher OR to P450 ratios) implying that the R144C change affects interaction of the P450 with OR. The rates of (S)-warfarin 7-hydroxylation by CYP2C9 and the R144C variant also exhibited differential dependence on salt concentration which further supported a difference in interaction with OR. When OR was bypassed and the hydroxylation was supported by cumene hydroperoxide, no difference in the rates of diclofenac 4'-hydroxylation was observed for CYP2C9 and the R144C variant regardless of OR to P450 ratio. However, for (S)-warfarin 7-hydroxylation, some OR-dependence was maintained even when the reaction was supported by cumene hydroperoxide. Finally, we compared CYP2C9 activity and CYP2C9 protein levels for human lymphoblast expressed (high OR to P450 ratio) to human liver microsomes using immunoblotting and enzyme selective substrates. Human liver microsomal CYP2C9 and human lymphoblast-expressed CYP2C9 showed comparable amounts of activity per unit enzyme. This final observation indicates that the high OR to P450 ratio is the preferred model and predicts that the R144C change in human liver microsomal CYP2C9 should markedly reduce the rates of substrate metabolism. The implications of these observations for the interpretation of results with cDNA-expressed enzymes is discussed.

DrugBank Data that Cites this Article

Pharmaco-genomics

Drug	Interacting Gene/Enzyme	Allele name	Genotypes	Defining change(s)	Type(s)	Description	Details
Phenytoin	Cytochrome P450 2C9 Gene symbol: CYP2C9 UniProt: P11712	CYP2C9*2	Not Available	430C>T (rs1799853)	Effect Inferred	Poor drug metabolizer, lower dose requirements	Details
Celecoxib	Cytochrome P450 2C9 Gene symbol: CYP2C9 UniProt: P11712	CYP2C9*2	Not Available	430C>T (rs1799853)	Effect Inferred	Poor drug metabolizer, lower dose requirements	Details
Clopidogrel	Cytochrome P450 2C9 Gene symbol: CYP2C9 UniProt: P11712	CYP2C9*2	Not Available	430C>T (rs1799853)	Effect Inferred	Poor drug metabolizer, lower dose requirements, higher risk for drug-drug interactions	Details
Acetylsalicylic acid	Cytochrome P450 2C9 Gene symbol: CYP2C9 UniProt: P11712	CYP2C9*2	Not Available	430C>T (rs1799853)	Effect Inferred	Poor drug metabolizer, lower dose requirements	Details
Glipizide	Cytochrome P450 2C9 Gene symbol: CYP2C9 UniProt: P11712	CYP2C9*2	Not Available	430C>T (rs1799853)	Effect Inferred	Poor drug metabolizer, lower dose requirements	Details
Tolbutamide	Cytochrome P450 2C9 Gene symbol: CYP2C9 UniProt: P11712	CYP2C9*2	Not Available	430C>T (rs1799853)	Effect Inferred	Poor drug metabolizer, lower dose requirements	Details