Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.6.5.2 (NQO1)
6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A photoaffinity analog of 4-hydroxycoumarin containing an azidobenzyl group at the 3-position and, if desired, carbon-14 or tritium radionuclides has been synthesized and characterized. This compound, 3-(p-azidobenzyl)-4-hydroxycoumarin, serves as an effective competitive inhibitor of the dicoumarol-sensitive NAD(P)H:quinone reductase (EC 1.6.99.2; DT-diaphorase) from rat liver, having an apparent inhibition constant of 6.6 x 10(-8) M, a value comparable to that observed for dicoumarol (1.7 x 10(-9) M), significantly lower than for Warfarin (3.5 x 10(-5) M) and well within the range required of an effective photoaffinity reagent. Irradiation of the reductase with ultraviolet light in the presence of the photoprobe resulted in the covalent labeling of up to 10% of the protein. Greater than 99% of the covalent incorporation is precluded by the addition of 15 microM dicoumarol, consistent with the specific labeling of the 4-hydroxycoumarin binding site of this enzyme by this photoaffinity reagent. Further evidence of a high degree of specificity is provided by the isolation and sequence analysis of the peptides covalently modified by this reagent. A single region within the protein was found to be labeled, with threonine 127 and tyrosine 128 being the only amino acid residues that were observed to be modified. These results, for the first time, define a portion of the 4-hydroxycoumarin binding site within a protein that has a well established sensitivity to this type of anticoagulant and, because dicoumarol serves as a competitive inhibitor for pyridine nucleotides in this enzyme, may also define a portion of this unusual pyridine nucleotide binding site. In addition, these results suggest that this reagent may be effective as a highly specific photoaffinity probe in the identification of other proteins that are similarly inhibited by 4-hydroxycoumarin derivatives, such as the microsomal enzymes associated with the vitamin K-dependent carboxylation system.
...
PMID:Synthesis of the photoaffinity probe 3-(p-azidobenzyl)-4-hydroxycoumarin and identification of the dicoumarol binding site in rat liver NAD(P)H:quinone reductase (EC 1.6.99.2). 170 34

In this in vivo study, the time-dependent effect of oral sodium warfarin was studied in male rats synchronized under a 12-hr light-dark cycle (light 0600-1800). Groups of 5 animals received an oral dose of 500 micrograms/kg of warfarin or saline at 0600 or 1800 and 1 mg/kg of vitamin K 8 hr later and the rats were sacrificed 240 min after vitamin K administration. The activities of the vitamin K reductase and vitamin K epoxide reductase were measured indirectly by determining the content of vitamin K1 and vitamin K epoxide reductase in the plasma and liver. The data obtained in control rats indicated that vitamin K and vitamin K 2,3 epoxide concentrations in plasma and liver were higher (P less than 0.05) at 1800 than at 0600. Warfarin had a greater (P less than 0.05) inhibitory effect on the vitamin K and vitamin K-epoxide reductases at 0600 compared to 1800; plasma levels of S- and R-warfarin did not vary with time of administration. The findings suggest that the activity of both reductases under control conditions, and the warfarin-induced inhibition of these enzymes varied depending on the time of drug administration.
...
PMID:Temporal variation in the effects of warfarin on the vitamin K cycle. 209 73

Our report presents data on maturation of the vitamin K-dependent carboxylation system in fetal and neonatal rat livers. This system which converts precursors of clotting factors II, VII, IX, X, protein S, and protein C to gamma-carboxylated proteins exhibited low gamma-carboxylation activity before birth. However, around the time of birth there was a sudden increase in all enzyme activities associated with the vitamin K-dependent carboxylation system. In 2-d neonatal rats these activities dropped to levels that were measured in fetal livers whereupon the activities had risen to adult levels in 7-d neonatal rats. However, the activities of the two pathways that provide the carboxylase with reduced vitamin KH2 cofactor were never as high as that measured in maternal livers. It appeared that the pathway which is insensitive to coumarin anticoagulant drugs matures later than the coumarin drug-sensitive pathway. This conclusion is supported by the finding of a late appearance in development of the vitamin K-reducing enzyme DT-diaphorase. Warfarin, when administered to the mother, affected the fetal livers at all stages of development studied (d 16-21). This was clearly demonstrated by vitamin K-dependent 14C-labeling of a 70-kD liver protein that has been shown previously to be a marker for the effect of this drug on the liver. The data demonstrate a similar mechanism of action of warfarin in fetal and neonatal rat livers and an ongoing maturation process of the vitamin K-dependent carboxylation system in these rats.
...
PMID:Vitamin K-dependent carboxylation in the developing rat: evidence for a similar mechanism of action of warfarin in fetal and adult livers. 250 52

Vitamin K-dependent carboxylase activity has been demonstrated in the crude microsomal fraction of the intima of bovine aortae. The procedure for the isolation of vessel wall carboxylase is a slight modification of the general preparation procedure for tissue microsomes. The highest activity of the non-hepatic enzyme was observed at 25 degrees C and hardly any NADH-dependent vitamin K reductase could be demonstrated. The optimal reaction conditions for both vessel wall as well as liver carboxylase were similar: 0.1 M-NaCl/0.05 M-Tris/HCl, pH 7.4, containing 8 mM-dithiothreitol, 0.4% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonic acid (CHAPS), 0.4 mM-vitamin K hydroquinone and 2 M-(NH4)2SO4. Warfarin inhibits the hepatic and non-hepatic carboxylase/reductase enzyme complex more or less to a similar degree. We have measured the apparent Km values for the following substrates: Phe-Leu-Glu-Glu-Leu ('FLEEL'), decarboxylated osteocalcin, decarboxylated fragment 13-29 from descarboxyprothrombin and decarboxylated sperm 4-carboxyglutamic acid-containing (Gla-)protein. The results obtained demonstrated that liver and vessel wall carboxylase may be regarded as isoenzymes with different substrate specificities. The newly discovered enzyme is the first vitamin K-dependent carboxylase which shows an absolute substrate specificity: FLEEL and decarboxylated osteocalcin were good substrates for vessel wall carboxylase, but decarboxylated fragment 13-29 and decarboxylated sperm Gla-protein were not carboxylated at all.
...
PMID:Isolation and partial characterization of a vitamin K-dependent carboxylase from bovine aortae. 349 40

Two procedures have been developed for the solubilization of vitamin K epoxide reductase from rat liver microsomal membranes using the detergent Deriphat 160 at pH 10.8. The methods are applicable to both normal and Warfarin-resistant-strain rat liver microsomes and yield material suitable for further purification. The preparations retain dithiothreitol-dependent vitamin K quinone reductase activity as well as vitamin K epoxide reductase and are free of vitamin K-dependent carboxylase and epoxidase activities. Optimal epoxide reductase activity is obtained at 0.1 M KCl and pH 9 in the presence of sodium cholate. Artifactual formation of vitamin K metabolites was eliminated through the use of mercuric chloride to remove excess dithiothreitol prior to extraction and metabolite assay. Using the solubilized enzyme, valid initial velocities were measured, and reproducible kinetic data was obtained. The substrate initial velocity patterns were determined and are consistent with a ping-pong kinetic mechanism. The kinetic parameters obtained are a function of the cholate concentration, but do not vary drastically from those obtained using intact microsomal membranes. At 0.8% cholate, the enzymes solubilized from normal Warfarin-sensitive- and Warfarin-resistant-strain rat livers exhibit respective values of Vmax = 3 and 0.75 nmol/min/g liver; Km for vitamin K epoxide = 9 and 4 microM; and Km for dithiothreitol of 0.6 and 0.16 mM.
...
PMID:Solubilization and characterization of vitamin K epoxide reductase from normal and warfarin-resistant rat liver microsomes. 669 43

The role of flavins in vitamin K function was assessed by examining blood coagulation and in vitro activities of hepatic vitamin K-dependent enzymes from control and riboflavin-deficient rats. One-stage prothrombin times and Factor VII activities were lower in flavin-deficient rats than in ad libitum or pair-fed controls. Fibrinogen, prothrombin, and Factor X activities were normal. Hepatic vitamin K-dependent carboxylase activity was severely depressed in flavin-deficient rats when assayed with [vitamin K + NADH] and somewhat depressed with reduced vitamin K (vitamin KH2) as substrate. One-hour flavin repletion appreciably restored [vitamin K + NADH]-dependent activity, but vitamin KH2-dependent activity was not restored even after 16 hours repletion. These results suggest that the carboxylating enzyme itself is not a flavoprotein, but that the microsomal NADH dehydrogenase required for [vitamin K + NADH]-dependent carboxylation is a flavoprotein. This dehydrogenase may differ from the cytosolic Warfarin-inhibitable 'DT-diaphorase' in that the activity of the latter, which is reduced 50% in flavin-deficient rats, is not at all restored by one-hour flavin repletion. Flavin status-dependent differences in NADH-dependent or vitamin KH2-dependent epoxidation of vitamin K paralleled differences in the carboxylase. Flavin deficiency had no effect on vitamin K 2,3-epoxide reductase activity nor on its inhibition by Warfarin.
...
PMID:Vitamin K-dependent reactions in rat liver: role of flavoproteins. 731 May 34

Dicumarol [3,3'-methylene-bis(4-hydroxycoumarin)] is a potent inhibitor of NAD(P)H:quinone oxidoreductase-1. Exposure of rat liver epithelial cells or of human skin fibroblasts to dicumarol resulted in a rapid and complete inhibition of connexin-43-dependent gap junctional intercellular communication (GJC). GJC was restored within 60min following removal of dicumarol. The concentration of dicumarol required for half maximal inhibition of GJC was 3muM, making dicumarol about 10-fold more effective in blocking GJC than 1-octanol and flufenamic acid, known inhibitors of GJC. Warfarin, a related coumarin derivative, also attenuated GJC, yet very high concentrations of 5-10mM were required. Dicumarol-induced downregulation of GJC was found not to be due to an interference with pathways enhancing the phosphorylation of connexin-43, such as epidermal growth factor receptor and extracellular signal-regulated kinase pathways. Rather, inhibition of GJC by dicumarol was paralleled by a reversible loss of a phosphorylated form ("P2") of connexin-43.
...
PMID:Dicumarol is a potent reversible inhibitor of gap junctional intercellular communication. 1563 23

The gamma-carboxyglutamate-containing proteins are a family of secreted vitamin K-dependent proteins in which some glutamyl residues are post-translationally modified to gamma-carboxyglutamic acid residues. A vitamin K-dependent gamma-glutamyl carboxylase enzyme catalyses this post-translational modification. The gamma-carboxylase reaction requires vitamin K in its reduced form, vitamin K hydroquinone, and generates gamma-carboxyglutamate and vitamin K 2,3,-epoxide which is then recycled back to the hydroquinone form by a vitamin K reductase system. Warfarin blocks the vitamin K cycle and hence inhibits the gamma-carboxylase reaction, and this property of Warfarin has led to its wide use in anticoagulant therapy. Until recently, interest in vitamin K-dependent proteins was mostly restricted to the field of hematology. However, the discovery that the anti-coagulant factor protein S and its structural homologue Gas6 (growth arrest-specific gene 6), two vitamin K-dependent proteins, are ligands for the Tyro3/Axl/Mer family of related tyrosine kinase receptors has opened up a new area of research. Moreover, the phenotypes associated with the invalidation of genes encoding vitamin K-dependent proteins or their receptors revealed their implication in regulating phagocytosis during many cell differentiation phenomena such as retinogenesis, neurogenesis, osteogenesis, and spermatogenesis. Additionally, protein S was identified as the major factor responsible for serum-stimulated phagocytosis of apoptotic cells. Therefore, the elucidation of the molecular mechanisms underlying the role of vitamin K-dependent proteins in regulating apoptotic cell phagocytosis may lead to a better understanding of the physiopathology of cell differentiation and could form the framework of new therapeutic strategies aiming at a selective targeting of cell phagocytosis associated pathologies.
...
PMID:[Gas-6 and protein S: vitamin K-dependent factors and ligands for the TAM tyrosine kinase receptors family]. 1793 90

Coumarins are of many different structures. They constitute an important class of pharmacological agents possessing a range of different physiological activities including anti-cancer, anti-oxidant, anti- inflammation, anti-HIV, anti-coagulant, anti-bacterial, analgesic and comparative immune-modulation. Recently, coumarins have attracted intense research interest. Of great interest is the possibility that this class of molecules could be a source of drugs for the therapy of several diseases. These include recent insights into inhibiting cell proliferation by interfering with mitotic spindle microtubule function, decrease Matrix Metalloproteinase (MMP) activity, block the cell cycle in the S or G2/M phases to interfere with processes of cell division, suppress O2(-) generation in leukocytes, inhibit different protein kinases, modulate the signalings, induce carcinogen-detoxifying enzymes glutathione S-transferases (GSTs) and/or NAD(P)H quinine oxidoreductase (NQO1), suppress the phosphorylation of Akt/PKB as a mechanism inhibiting inflammation, progress in structure modification to increase in anti-fungal action, to broaden against bacteria spectrum, to enhance inhibiting activities of nitric oxide synthase (NOS) and cyclooxygenase (COX), to strengthen anti-oxidant activity and to exhibite a much higher cytotoxicity against human umbilical vein endothelial cell (HUVEC). With fewer non-hemorrhagic side effects than the indanedione derivatives, they can be applied as an oral anticoagulant commonly for preventing venous thromboembolism following orthopedic surgery, recurrent myocardial infarction and the treatment of systemic embolism in atrial fibrillation, together with the significant advances in the basis of drug action. It is therefore useful to build up some correlations with the data available in order to better explore the molecular and cellular mechanism of coumarin action in the treatment of diseases. This review will focus on recent advances in molecular and cellular mechanisms of coumarin action involved with the relationship between structure and activity.
...
PMID:The structure and pharmacological functions of coumarins and their derivatives. 1975 20

Warfarin demonstrates a wide interindividual variability in response that is mediated partly by variants in cytochrome P450 2C9 (CYP2C9) and vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1). It is not known whether variants in calumenin (CALU) (vitamin K reductase regulator) have an influence on warfarin dose requirements. We resequenced CALU regions in a discovery cohort of dose outliers: patients with high (>90th percentile, n = 55) or low (<10th percentile, n = 53) warfarin dose requirements (after accounting for known genetic and nongenetic variables). One CALU variant, rs339097, was associated with high doses (P = 0.01). We validated this variant as a predictor of higher warfarin doses in two replication cohorts: (i) 496 patients of mixed ethnicity and (ii) 194 African-American patients. The G allele of rs339097 (the allele frequency was 0.14 in African Americans and 0.002 in Caucasians) was associated with the requirement for a 14.5% (SD +/- 7%) higher therapeutic dose (P = 0.03) in the first replication cohort and a higher-than-predicted dose in the second replication cohort (allele frequency 0.14, one-sided P = 0.03). CALU rs339097 A>G is associated with higher warfarin dose requirements, independent of known genetic and nongenetic predictors of warfarin dose in African Americans.
...
PMID:A polymorphism in the VKORC1 regulator calumenin predicts higher warfarin dose requirements in African Americans. 2020 May 17


1 2 Next >>

---