The Active Site of Vitamin K and the Role of the Vitamin K-Dependent Carboxylase

Naganathan, Sriram; Hershline, Roger; Ham, Seung Wook; Dowd, Paul

doi:10.1021/ja00101a003

Cited by 26 publications

(21 citation statements)

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“…vitamin K is observed. This nonenzymatic, chemical change constitutes a model for the oxygenation of vitamin KH-to vitamin K oxide that takes place at the active site of the enzyme, and provides nonenzymatic support for the proposal that deprotonation of vitamin KH2 at the carboxylase active site is the critical step in the oxygenation leading to vitamin K oxide (31). This model oxygenation reaction (Eq.…”

Section: -mentioning

confidence: 55%

“…If one examines the parent ion cluster at m/e values of 466, 467, and 468 in the mass spectrum of unlabeled vitamin K oxide, the ratio of peak intensities is 100:34:6. These relative intensities are entirely appropriate for the natural abundance levels of one and two atoms of l3C in vitamin K oxide, which has 31 (26). While the M' (parent ion) + 1 peak at m/e 469 is completely normal in intensity relative to the parent peak at m/e 468, the M+ + 2 peak at m/e 470 is four times more intense than the calculated value (26).…”

Section: -mentioning

confidence: 92%

“…Following this analysis, we have carried out 1802 labeling experiments with the carboxylase in a rat liver microsomal preparation and find, in the |mie 466 0 + |mle 306| course of 12 trials, 17 + 1.4% (standard deviation) incorporation of a second atom of 180 into the product vitamin K oxide (26,31,33,34).…”

Section: -mentioning

confidence: 99%

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Vitamin K and Energy Transduction: A Base Strength Amplification Mechanism

Dowd

Hershline

Ham

et al. 1995

Science

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135

106

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Energy transfer provides an arrow in the metabolism of living systems. Direct energetic coupling of chemical transformations, such that the free energy generated in one reaction is channeled to another, is the essence of energy transfer, whereas the purpose is the production of high-energy chemical intermediates. Vitamin K provides a particularly instructive example of energy transfer. A key principle at work in the vitamin K system can be termed "base strength amplification." In the base strength amplification sequence, the free energy of oxygenation of vitamin K hydroquinone (vitamin KH2) is used to transform a weak base to a strong base in order to effect proton removal from selected glutamate (Glu) residues in the blood-clotting proteins.

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Section: -mentioning

confidence: 55%

Section: -mentioning

confidence: 92%

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Vitamin K and Energy Transduction: A Base Strength Amplification Mechanism

Dowd

Hershline

Ham

et al. 1995

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135

106

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“…The vitamin K-dependent carboxylase and the other enzymes of the vitamin K cycle were obtained from rat liver microsomes (24,25). The uptake of 14C02 by the synthetic pentapeptide substrate FLEEI, as a function of inhibitor concentration, was used as a measure of carboxylase activity and its inhibition.…”

Section: Resultsmentioning

confidence: 99%

“…ylase contains two active site cysteine residues (26)(27)(28)(29)(30)(31)(32). One sulfhydryl group initiates the oxygenation of vitamin K hydroquinone to vitamin K oxide by proton abstraction from vitamin K hydroquinone (24); the second sulfhydryl group may assist in binding carbon dioxide (24).…”

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On the mechanism of the anticlotting action of vitamin E quinone.

Dowd

Zheng

1995

Proc. Natl. Acad. Sci. U.S.A.

115

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Vitamin E in the reduced, a-tocopherol form shows very modest anticlotting activity. By contrast, vitamin E quinone is a potent anticoagulant. This observation may have significance for field trials in which vitamin E is observed to exhibit beneficial effects on ischemic heart disease and stroke. Vitamin E quinone is a potent inhibitor of the vitamin K-dependent carboxylase that controls blood clotting. A newly discovered mechanism for the inhibition requires attachment of the active site thiol groups of the carboxylase to one or more methyl groups on vitamin E quinone. The results from a series of model reactions support this interpretation of the anticlotting activity associated with vitamin E.With the success of recent field trials of vitamin E, and the attendant promise of forestalling the onset of heart attack and stroke (1, 2), it becomes important to understand the molecular mechanistic basis of this beneficent physiological activity. Since vitamin E is an excellent antioxidant (3-7) and radical inhibitor (8-11), these properties have been used, in general fashion, to interpret its physiological activity and its possible role in living systems (3)(4)(5)(6)(7)(8)(9)(10)(11)(12).It is known that vitamin E has anticoagulant properties (13-18), but this attribute has not been applied to understanding its physiological action. The recent Finnish study of male heavy smokers (19) found little efficacy of vitamin E and 13-carotene in preventing the occurrence of cancer, but the study did show the positive potential of vitamin E in cardiovascular therapy. There were clear benefits among the participants for ischemic heart disease and ischemic stroke, but, significantly, vitamin E acted to the detriment of those prone to hemorrhagic stroke (19). Accordingly, we suggest that the anticoagulant properties of vitamin E be included when evaluating the results of such trials.What are the anticoagulant properties of vitamin E, and why have they not been used in interpreting its physiologic role? For one, there has been some confusion about which oxidation states of vitamin E are effective anticoagulants, or, alternatively, which derivatives of vitamin E interdict the vitamin K-dependent clotting cycle and how effectively (20)(21)(22)(23). In response to the second part of the question, no mechanistic underpinning for the anticlotting properties of vitamin E has been developed, nor has there been any speculation regarding molecular mechanisms by which vitamin E might act as an inhibitor of the vitamin K-dependent carboxylase that is required to activate the enzymes of the blood clotting cascade. This paper will address both issues. ResultsThe vitamin K-dependent carboxylase and the other enzymes of the vitamin K cycle were obtained from rat liver microsomes (24,25). The uptake of 14C02 by the synthetic pentapeptide substrate FLEEI, as a function of inhibitor concentration, was used as a measure of carboxylase activity and its inhibition. The Vitamin E quinone 2 production of vitamin K oxide was conveniently monitor...

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A short and convenient synthesis of [1-18O] and [4-18O] vitamin K1

Boullais

Delvallee

1998

J Label Compd Radiopharm

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Vitamin K1 was quantitatively reduced by Na2S2O4 to dihydrovitamin K1 (2). The hydroquinone 2 was partially methylated by CH3I/K2CO3 to give a mixture of 1 and 4 monomethylethers which were separated by HPLC. Each monoether was oxidized by ceric ammonium nitrate in the presence of [18O] H2O to afford the specifically labelled [1‐18O] or [4‐18O] vitamin K1 with isotopic enrichments of 93–95%. © 1998 John Wiley & Sons, Ltd.

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The Active Site of Vitamin K and the Role of the Vitamin K-Dependent Carboxylase

Cited by 26 publications

References 1 publication

Vitamin K and Energy Transduction: A Base Strength Amplification Mechanism

Vitamin K and Energy Transduction: A Base Strength Amplification Mechanism

On the mechanism of the anticlotting action of vitamin E quinone.

A short and convenient synthesis of [1-18O] and [4-18O] vitamin K1

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