Vitamin K epoxide reductase activity in the metabolism of epoxides

SummaryThe gene encoding vitamin K epoxide reductase complex subunit 1 (VKORC1), a component of the enzyme that is the therapeutic target site for warfarin, has recently been identified. In order to investigate the relationship betweenVKORC1 and warfarin dose response, we studied theVKORC1 gene (VKORC1) in patients with warfarin resistance. From a study group of 820 patients, we identified 4 individuals who required more than 25 mg of warfarin daily for therapeutic anticoagulation.Three of these had serum warfarin concentrations within the therapeutic range of 0.7–2.3 mg/l and showed wild-type VKORC1 sequence. The fourth warfarin resistant individual had consistently high ( ≥ 5.7 mg/l) serum warfarin concentrations, yet had no clinically discernible cause for warfarin resistance. VKORC1 showed a heterozygous 196G→ A transition that predicted aVal66Met substitution in the VKORC1 polypeptide. This transition was also identified in 2 asymptomatic family members who had never received warfarin.These individuals had normal vitamin-K dependent coagulation factor activities and undetectable serum PIVKAII and vitamin K 1 2,3 epoxide suggesting that their basal vitamin K epoxide reductase activity was not adversely affected by the VKORC1 Val66Met substitution.The association between a nucleotide transition in VKORC1 and pharmacodynamic warfarin resistance supports the hypothesis that VKORC1 is the site of action of warfarin and indicates that VKORC1 sequence is an important determinant of the warfarin dose response.

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Warfarin inhibition of hepatic vitamin K epoxide reductase activity in warfarin-susceptible and -resistant house mice (Mus domesticus)

Pesticide Biochemistry and Physiology ◽

10.1016/0048-3575(92)90010-w ◽

1992 ◽

Vol 44 (1) ◽

pp. 68-73 ◽

Cited By ~ 5

Author(s):

A.D. MacNicoll ◽

R.H. Dean

Keyword(s):

Vitamin K ◽

Reductase Activity ◽

House Mice ◽

Mus Domesticus ◽

Vitamin K Epoxide Reductase ◽

Epoxide Reductase

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Microsomal lipoamide reductase provides vitamin K epoxide reductase with reducing equivalents

Biochemical Journal ◽

10.1042/bj2970277 ◽

1994 ◽

Vol 297 (2) ◽

pp. 277-280 ◽

Cited By ~ 21

Author(s):

H H W Thijssen ◽

Y P G Janssen ◽

L T M Vervoort

Keyword(s):

Vitamin K ◽

Lipoic Acid ◽

Reductase Activity ◽

Vitamin K Epoxide Reductase ◽

Vitamin K Cycle ◽

Redox Active ◽

Starting Point ◽

Epoxide Reductase ◽

Triton X ◽

Reducing Equivalents

This study was undertaken to search for the endogenous dithiol cofactor of the reductases of the vitamin K cycle. As a starting point, the redox-active lipophilic endogenous compounds lipoic acid and lipoamide were looked at. The study shows that microsomes contain NADH-dependent lipoamide reductase activity. Reduced lipoamide stimulates microsomal vitamin K epoxide reduction with kinetics comparable with those for the synthetic dithiol dithiothreitol (DTT). Reduced lipoic acid shows higher (4-fold) Km values. No reductase activity with lipoic acid was found to be present in microsomes or cytosol. The reduced-lipoamide-stimulated vitamin K epoxide reductase is as sensitive to warfarin and salicylate inhibition as is the DTT-stimulated one. Both vitamin K epoxide reductase and lipoamide reductase activity are recovered in the rough microsomes. NADH/lipoamide-stimulated vitamin K epoxide reduction is uncoupled by traces of Triton X-100, suggesting that microsomal lipoamide reductase and vitamin K epoxide reductase are associated. The results suggest that the vitamin K cycle obtains reducing equivalents from NADH through microsomal lipoamide reductase.

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Overexpression of protein disulfide isomerase enhances vitamin K epoxide reductase activity

Biochemistry and Cell Biology ◽

10.1139/bcb-2021-0441 ◽

2022 ◽

Author(s):

Thomas Chetot ◽

Etienne Benoit ◽

Véronique Lambert ◽

Virginie Lattard

Keyword(s):

Vitamin K ◽

Protein Disulfide Isomerase ◽

Reductase Activity ◽

Functional Characterization ◽

Hek293 Cells ◽

Vitamin K Epoxide Reductase ◽

Disulfide Isomerase ◽

Vitamin K Cycle ◽

Epoxide Reductase ◽

Protein Disulfide

Vitamin K epoxide reductase (VKOR) activity is catalyzed by the VKORC1 enzyme. It is the target of vitamin K antagonists (VKA). Numerous mutations of VKORC1 have been reported and have been suspected to confer resistance to VKA and/or affect its velocity. Nevertheless, the results between studies have been conflicting, the functional characterization of these mutations in a cell system being complex due to the interweaving of VKOR activity in the vitamin K cycle. In this study, a new cellular approach was implemented to globally evaluate the vitamin K cycle in the HEK293 cells. This global approach was based on the vitamin K quinone/vitamin K epoxide (K/KO) balance. In the presence of VKA or when the VKORC1/VKORC1L1 were knocked out, the K/KO balance decreased significantly due to an accumulation of vitamin KO. On the contrary, when VKORC1 was overexpressed, the balance remained unchanged, demonstrating a limitation of the VKOR activity. This limitation was shown to be due to an insufficient expression of the activation partner of VKORC1, as overexpressing the protein disulfide isomerase (PDI) overcomes the limitation. This study is the first to demonstrate a functional interaction between VKORC1 and the PDI enzyme.

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