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)

NO synthase (NOS; EC 1.14.23) catalyzes the conversion of L-arginine into L-citrulline and a guanylyl cyclase-activating factor (GAF) that is chemically identical with nitric oxide or a nitric oxide-releasing compound (NO). Similar to the other isozymes of NOS that have been characterized to date, the soluble and Ca2+/calmodulin-regulated type I from rat cerebellum (homodimer of 160-kDa subunits) is dependent on NADPH for catalytic activity. The enzyme also possesses NADPH diaphorase activity in the presence of the electron acceptor nitroblue tetrazolium (NBT). We investigated the requirements of NOS and its content of the proposed additional cofactors tetrahydrobiopterin (H4biopterin) and flavins, further characterized the NADPH diaphorase activity, and quantified the NADPH binding site(s). Purified NOS type I Ca2+/calmodulin-independently bound the [32P]2',3'-dialdehyde analogue of NADPH (dNADPH), which, at near Km concentrations during 3-min incubations was utilized as a substrate and at higher concentrations or after prolonged incubations and cross-linking inhibited NOS activity. The NADPH diaphorase activity was Ca2+/calmodulin-independent, required higher NADPH concentrations than NOS activity, and was affected by dNADPH to a lesser degree. Divalent cations interfered with the diaphorase assay. Per dimer, native NOS contained about 1 mol each of H4biopterin, FAD, and FMN, classifying it as a biopteroflavoprotein, and incorporated 1 mol of dNADPH. No dihydrobiopterin (H2biopterin), biopterin, or riboflavin was detected. These findings suggest that NOS may share cofactors between two identical subunits via high-affinity binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Ca2+/calmodulin-dependent NO synthase type I: a biopteroflavoprotein with Ca2+/calmodulin-independent diaphorase and reductase activities. 137 27

Calcineurin, a multifunctional Ca2+ (divalent cations)-dependent calmodulin-stimulated phosphoprotein phosphatase, has been reported to be present in the striatal neurons which project to the globus pallidus and the substantia nigra. In the present study, we examined what types of cells in the rat striatum express calcineurin. The calcineurin-positive neurons were of medium size (mean diameter of 16 microns) and constituted about 60-70% of the total neuronal population in the striatum. Under light microscopy, the calcineurin-positive neurons had round, triangular, or polygonal cell bodies with a relatively small amount of cytoplasm. Electron microscopic examination of 20 randomly selected striatal calcineurin-immunoreactive neurons revealed that their nuclei did not show any invaginations or intranuclear inclusions. The calcineurin-positive neurons were characterized by Golgi impregnation as the densely spinous type. On the other hand, it was demonstrated that calcineurin-positive neurons are a separate population from the diisopropylfluorophosphate-acetylcholinesterase-positive cells or nicotinamide adenine dinucleotide phosphate diaphorase-positive cells, by means of the combination of immunocytochemistry and enzyme histochemistry. In addition, simultaneous localization of calcineurin and substance P in a single cell was observed in some striatal neurons using a double immunostaining method. On the basis of these findings, it was considered that most calcineurin-immunoreactive neurons in the rat striatum may be classified as medium-size densely spiny neurons.
...
PMID:Morphological characterization of the rat striatal neurons expressing calcineurin immunoreactivity. 244 61

The activity of an nitric oxide synthase in the deutocerebrum of the crayfish Pacifastacus leniusculus was investigated with histochemical and biochemical methods. By using the NADPH-diaphorase histochemical reaction, known as a selective marker for NO synthase in mammals, it was possible to localize specific neuronal elements in the crayfish. Pronounced diaphorase-staining was observed in peripheral olfactory sensory cells and in the neuropil of the olfactory lobes. Less intense diaphorase-staining also occurred in other deutocerebral neuropils, such as the accessory lobes, the lateral antennular neuropil and in the deutocerebral commissure neuropil. The biochemical assay revealed a calcium/calmodulin-dependent formation of citrulline from L-arginine in brain homogenate. It was also possible to show that the selective NO synthase inhibitor L-NOARG decreased the formation of citrulline. These data indicate a role for NO as an intercellular messenger in the crayfish.
...
PMID:NADPH-diaphorase histochemistry and nitric oxide synthase activity in deutocerebrum of the crayfish, Pacifastacus leniusculus (Crustacea, Decapoda). 752 13

The salivary glands of the hematophagous insect, Rhodnius prolixus, contain a nitrosylhemeprotein that dissociates its ligand, NO, to the host tissues while the insect is searching for a blood meal. We now report a salivary nitric oxide synthase activity in this insect. The activity is dependent on NADPH, FAD, tetrahydrobiopterin, calmodulin, Ca2+, and converts arginine to citrulline while producing vasorelaxing activity. Molecular sieving indicates a molecular weight of 185 kDa, coeluting with a diaphorase activity. Results indicate similarity of this insect activity to the vertebrate constitutive NO synthase, suggesting NO synthesis is an evolutionary old biological pathway.
...
PMID:Nitric oxide synthase activity from a hematophagous insect salivary gland. 768 81

The distribution of the nicotinamide adenine dinucleotide phosphate-(NADPH) diaphorase reaction, an indicator of nitric oxide synthase activity, was studied in the freshwater planarian Dugesia tigrina (Platyhelminthes). The reaction was restricted to the pharynx, where the inner epithelium was intensely stained and the outer epithelium moderately stained. Neurons that innervated the pharynx were also stained. The enzyme activity was studied by high pressure liquid chromatographic quantitation of the formed citrulline. The presumed nitric oxide synthase was dependent on NADPH, whereas no dependency on Ca2+ and calmodulin could be detected. Tetrahydrobiopterin increased the activity about fivefold to 218.2+/-24.9 fmol/mg protein per min. Nomega-nitro-l-arginine depressed the enzyme activity by about 80%. The results indicate that nitric oxide has a role in the feeding behavior of planarians.
...
PMID:Nitric oxide synthase in the pharynx of the planarian Dugesia tigrina. 892 43

The presence of nitric oxide synthase (NOS) in neuronal elements expressing the calcium-binding proteins calretinin (CR) and parvalbumin (PV) was studied in the rat main olfactory bulb. CR and PV were detected by using immunocytochemistry and the nitric oxide (NO) -synthesizing cells were identified by means of the reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) direct histochemical method. The possible coexistence of NADPH-diaphorase and each calcium-binding protein marker was determined by sequential histochemical-immunohistochemical double-labeling of the same sections. Specific neuronal populations were positive for these three markers. A subpopulation of olfactory fibers and olfactory glomeruli were positive for either NADPH-diaphorase or CR. In the most superficial layers, groups of juxtaglomerular cells, superficial short-axon cells and Van Gehuchten cells demonstrated staining for all three markers. In the deep regions, abundant granule cells were NADPH-diaphorase- and CR-positive and a few were PV-immunoreactive. Scarce deep short-axon cells demonstrated either CR-, PV-, or NADPH-diaphorase staining. Among all these labeled elements, no neuron expressing CR or PV colocalized NADPH-diaphorase staining. The present data contribute to a more detailed classification of the chemically- and morphologically-defined neuronal types in the rodent olfactory bulb. The neurochemical differences support the existence of physiologically distinct groups within morphologically homogeneous populations. Each of these groups would be involved in different modulatory mechanisms of the olfactory information. In addition, the absence of CR and PV in neuronal groups displaying NADPH-diaphorase, which moreover are calmodulin-negative, indicate that the regulation of NOS activity in calmodulin-negative neurons of the rat olfactory bulb is not mediated by CR or PV.
...
PMID:Calretinin- and parvalbumin-immunoreactive neurons in the rat main olfactory bulb do not express NADPH-diaphorase activity. 941 7

6-Anilino-5,8-quinolinedione (LY83583) has been widely used as an agent to reduce levels of nitric oxide (NO)-dependent cGMP in tissues. We report here that suppression of NO formation and production of superoxide during enzymatic reduction of LY83583 by neuronal NO synthase appeared to be potentially involved in the pharmacological action caused by LY83583. LY83583 suppressed neuronal NO synthase activity of 20,000 x g rat cerebellar supernatant preparation in a concentration-dependent manner (IC50 value = 12.9 microM). A kinetic study revealed that LY83583 is a competitive inhibitor with respect to NADPH, with a Ki value of 2.57 microM. With purified neuronal NO synthase it was found that LY83583 was a potent inhibitor of NO formation by the enzyme and served as efficient substrate for reduction with a specific activity of 173 nmol of NADPH oxidized per mg of protein per minute. The reductase activity was stimulated about 19.8-fold by addition of CaCl2/calmodulin, indicating that the presence of CaCl2/calmodulin is essential to express maximal activity of LY83583 reduction. Although LY83583 was a good substrate for both NADPH-cytochrome P450 reductase (P450 reductase) and DT-diaphorase, these flavin enzymes-catalyzed reductions of LY83583 were less than the neuronal NO synthase-mediated reduction in the presence of CaCl2/calmodulin. Enzymatic generation of superoxide during reduction of LY83583 by neuronal NO synthase, P450 reductase or DT-diaphorase was confirmed by electron spin resonance (ESR) experiments. Thus the present results indicate that a benzoquinone derivative LY83583 appears to interact with the P450 reductase domain on neuronal NO synthase, resulting in inhibition of NO formation and superoxide generation, which is involved in suppression of intracellular cGMP content.
...
PMID:Inhibition of nitric oxide formation and superoxide generation during reduction of LY83583 by neuronal nitric oxide synthase. 985 88

We colocalized nitric oxide synthase (NOS) activity in epithelial cells that surround the salivary gland duct in female Dermacentor variabilis with NADPH diaphorase histochemistry and immunohistochemistry using a polyclonal anti-endothelial NOS. Using size-exclusion chromatography, a fraction with a molecular mass of about 185 kDa that had diaphorase activity was eluted from tick salivary gland homogenate. This fraction converted arginine to citrulline with the production of nitric oxide (NO), which was detected by using electron spin resonance spectroscopy. The complete activity of the diaphorase fraction was dependent on NADPH, FAD, tetrahydrobiopterin, calmodulin, (CaM), and Ca(2+), but was not dependent on dithiothreitol. The arginine analog N(G)-monomethyl-L-arginine inhibited the activity of this fraction. NO and arginine activated soluble guanylate cyclase to produce cGMP in dopamine-stimulated isolated salivary glands. Dopamine-stimulated isolated salivary glands treated with tick saline containing either EDTA, the NOS inhibitor N(G)-nitro-L-arginine methyl ester, or the calcium/CaM binding inhibitor W-7 showed no increase in cGMP. The NO donor sodium nitroprusside significantly increased cGMP levels in unstimulated isolated salivary glands. A possible function for NO in salivation by this ixodid tick is discussed.
...
PMID:Nitric oxide synthase and cGMP activity in the salivary glands of the American dog tick Dermacentor variabilis. 1067 47

Flavin electron transferases can catalyze one- or two-electron reduction of quinones including bioreductive antitumor quinones. The recombinant neuronal nitric oxide synthase (nNOS) reductase domain, which contains the FAD-FMN prosthetic group pair and calmodulin-binding site, catalyzed aerobic NADPH-oxidation in the presence of the model quinone compound menadione (MD), including antitumor mitomycin C (Mit C) and adriamycin (Adr). Calcium/calmodulin (Ca2+/CaM) stimulated the NADPH oxidation of these quinones. The MD-mediated NADPH oxidation was inhibited in the presence of NAD(P)H:quinone oxidoreductase (QR), but Mit C- and Adr-mediated NADPH oxidations were not. In anaerobic conditions, cytochrome b5 as a scavenger for the menasemiquinone radical (MD*-) was stoichiometrically reduced by the nNOS reductase domain in the presence of MD, but not of QR. These results indicate that the nNOS reductase domain can catalyze a only one-electron reduction of bivalent quinones. In the presence or absence of Ca2+/CaM, the semiquinone radical species were major intermediates observed during the oxidation of the reduced enzyme by MD, but the fully reduced flavin species did not significantly accumulate under these conditions. Air-stable semiquinone did not react rapidly with MD, but the fully reduced species of both flavins, FAD and FMN, could donate one electron to MD. The intramolecular electron transfer between the two flavins is the rate-limiting step in the catalytic cycle [H. Matsuda, T. Iyanagi, Biochim. Biophys. Acta 1473 (1999) 345-355). These data suggest that the enzyme functions between the 1e- <==> 3e- level during one-electron reduction of MD, and that the rates of quinone reductions are stimulated by a rapid electron exchange between the two flavins in the presence of Ca2+/CaM.
...
PMID:One-electron reduction of quinones by the neuronal nitric-oxide synthase reductase domain. 1092 3

Nitric oxide (NO) may play a central role in controlling renal hemodynamics and renal salt excretion. Thus, several investigations focused on localization and function of nitric oxide synthase (NOS) isoforms in the mammalian kidney. Although studies of amphibians have contributed significantly to the elucidation of renal physiology, NOS has not been investigated in the amphibian kidney. Therefore, we characterized NOS and reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase biochemically and, furthermore, visualized putative NO-producing cells in the kidney of the clawed frog, Xenopus laevis. Our results indicate that NADPH-diaphorase activity correlates with NOS activity. Both enzyme activities eluted at 225 mM NaCl on a diethylaminoethanol anion exchange column and had an apparent molecular weight of 235 kDa, as estimated on an S-300 Sephacryl column. In addition, these enzymes were sensitive to Ca2+ and NADPH, but insensitive to calmodulin antagonists (trifluoperazine, W-13) or omission of calmodulin from the reaction medium. The molecular identity of NOS in Xenopus kidney extract was estimated using polymerase chain reaction. Primers to Xenopus neuronal NOS hybridized to a transcript in Xenopus kidney homogenate. NADPH-diaphorase histochemistry revealed staining in the neck segment, distal tubules, collecting segment, and peritoneal funnels. NOS-immunoreactive material was visualized in distal tubules. These results indicate that Xenopus kidney contains at least neuronal NOS, but may contain an additional NOS isoform, which is less calmodulin sensitive.
...
PMID:NADPH-diaphorase activity and nitric oxide synthase activity in the kidney of the clawed frog, Xenopus laevis. 1099 86


1 2 Next >>

---