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

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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)
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PMID:Ca2+/calmodulin-dependent NO synthase type I: a biopteroflavoprotein with Ca2+/calmodulin-independent diaphorase and reductase activities. 137 27

Nitric oxide, a simple gas which serves as a neurotransmitter in the CNS, has been proposed to serve as an interneuronal second messenger in olfactory transduction. However, the role of nitric oxide in olfaction has been questioned by experiments in which nitric oxide synthase, the enzyme that generates nitric oxide, could not be localized to the olfactory epithelium. We have localized nitric oxide synthase to the olfactory neurons in adult rat and catfish olfactory epithelia using a modified nicotinamide adenine dinucleotide phosphate diaphorase technique. In the rat, staining was also found in cells with morphology reminiscent of microvillar olfactory cells. In contrast, the respiratory epithelium and the sustentacular cells in the olfactory epithelium displayed no staining. The nicotinamide adenine dinucleotide phosphate diaphorase reaction, which has been shown to co-localize with immunohistochemical staining for nitric oxide synthase in the brain, was stimulated by addition of the nitric oxide synthase substrate L-arginine, and was inhibited by the nitric oxide synthase inhibitor L-NG-nitro arginine, indicating that staining was specific for nitric oxide synthase. Unilateral bulbectomy, which causes degeneration of mature olfactory neurons on the bulbectomized size, markedly reduced nicotinamide adenine dinucleotide phosphate diaphorase staining. These observations were substantiated by biochemical assays for nitric oxide synthase by monitoring the production of [3H]-L-citrulline from [3H]-L-arginine. This is the first demonstration of specific NADPH diaphorase staining of mature olfactory neurons in rat and catfish olfactory epithelial suggesting the presence of nitric oxide synthase in these cells. Our histological and biochemical findings, in conjunction with data from other research, are supportive of a role for nitric oxide synthase in olfactory function.
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PMID:NADPH diaphorase staining suggests localization of nitric oxide synthase within mature vertebrate olfactory neurons. 754 62

Neurons that synthesize nitric oxide from arginine produce stoichiometric amounts of citrulline. We investigated whether nitric oxide-releasing enteric neurons have the capacity to recycle citrulline to arginine and thereby sustain nitrergic neurotransmission. Argininosuccinate synthetase-like immunoreactivity and argininosuccinate lyase-like immunoreactivity, enzymes capable of citrulline to arginine conversion, were both localized in discrete populations of myenteric and submucosal neurons in the canine proximal colon. Argininosuccinate synthetase-like immunoreactivity and argininosuccinate lyase-like immunoreactivity co-localized with neuronal beta-nicotinamide adenine dinucleotide phosphate diaphorase staining, a marker for nitric oxide synthase. The functional significance of argininosuccinate synthetase-like immunoreactivity and argininosuccinate lyase-like immunoreactivity was shown by testing the effects of exogenous citrulline on responses to enteric inhibitory nerve stimulation, which were assessed by measuring contractions, inhibitory junction potentials and electrical slow waves. As shown previously, arginine analogues (L-nitroarginine methyl ester or L-nitroarginine; 100 microM) inhibited nitric oxide-dependent responses, and excess L-arginine restored inhibitory responses. Citrulline alone (0.1-2 mM) had no effect on nitrergic transmission under control conditions, but in the presence of L-nitroarginine methyl ester or L-nitroarginine, citrulline (0.1-2 mM) restored nitrergic transmission in a concentration-dependent manner. Other neutral amino acids (L-serine, L-leucine) did not mimic the effects of citrulline. Taken together, these data suggest that enteric nitrergic neurons have the enzymatic apparatus and functional capability of recycling citrulline to arginine.
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PMID:Recycling of L-citrulline to sustain nitric oxide-dependent enteric neurotransmission. 854 1

Copper complexes with superoxide dismutase (SOD) activity show a wide range of pharmacological activities. We have investigated the effect of ([N,N'-bis(2-pyridylmethylene)-1,4-butanediamine]-(N,N',N", N"')]-Cu(II)-chloride (Cu-PuPy) and ([N,N'-bis(2-pyridyl-phenyl)methylene-1,4-butanediamine]-(N,N',N", N"'))-Cu(II)-chloride (Cu-PuPhePy) on the multiple catalytic functions of rat brain NO synthase (NOS). Both drugs inhibited the formation of L-citrulline as well as the enzymatic reduction of cytochrome c. The uncoupled oxidation of NADPH, catalyzed by neuronal NOS in the absence of L-arginine, was inhibited by Cu-PuPy but stimulated by Cu-PuPhePy, suggesting that the phenyl-substituted compound acts as a parasitic electron acceptor. Our data identify copper complexes with SOD mimicking activity as a novel class of neuronal NOS inhibitors blocking the reductase (diaphorase) activity of the enzyme.
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PMID:Structural and functional analogs of CuZn superoxide dismutase inhibit rat brain nitric oxide synthase by interference with the reductase (diaphorase) domain. 873 37

An anatomical basis was sought for the postulated roles of nitric oxide (NO) as a labile transcellular messenger in the dorsal vagal complex (NTS-X). The diaphorase activity of NO synthase was used as a marker of neurons in NTS-X that are presumed to convert L-arginine to L-citrulline and NO. Nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) staining patterns in the nucleus tractus solitarii (NTS) were spatially related to terminal sites of primary visceral afferents from 1) orosensory receptors (e.g., rostral-central nucleus); 2) soft palate, pharynx, larynx, and tracheobronchial tree (e.g., dorsal, intermediate, and interstitial nuclei); 3) esophagus (nucleus centralis); 4) stomach (nucleus gelatinosus); 5) hepatic and coeliac nerves (nucleus subpostrema); and 6) carotid body and baroreceptors (medial commissural and dorsal-lateral nuclei). Primary visceral afferents were identified as sources of NADPHd-stained fiber plexuses in the NTS-X based on three findings: 1) the presence of NADPHd in nodose ganglion cells with morphological features of first-order sensory relay neurons; 2) retrograde transport of Fluoro-Gold (FG) or cholera toxin B (CT-B) from NTS-X to NADPHd-positive nodose ganglion neurons; and 3) striking reductions of NADPHd-stained processes within primary vagal projection fields ipsilateral to unilateral nodose ganglionectomy. A central origin of NADPHd-stained processes in NTS-X was identified in the medial parvicellular subdivision of the paraventricular hypothalamic nucleus. We conclude that NO of peripheral and central origin may modulate viscerosensory signal processing in the NTS-X and autonomic reflex function.
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PMID:Central and primary visceral afferents to nucleus tractus solitarii may generate nitric oxide as a membrane-permeant neuronal messenger. 878 75

The presence and coexistence of calbindin D-28k-immunoreactivity (ir) and nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase activity (a marker of neurons that are presumed to convert L-arginine to L-citrulline and nitric oxide) were examined in the glossopharyngeal and vagal sensory ganglia (jugular, petrosal and nodose ganglia) of the rat. Calbindin D-28k-ir nerve cells were found in moderate and large numbers in the petrosal and nodose ganglia, respectively. Some calbindin D-28k-ir nerve cells were also observed in the jugular ganglion. NADPH-diaphorase positive nerve cells were localized to the jugular and nodose ganglia and were rare in the petrosal ganglion. A considerable portion (33-51%) of the NADPH-diaphorase positive neurons in these ganglia colocalized calbindin D-28k-ir. The presence and colocalization of calbindin D-28k-ir and NADPH-diaphorase activity in neurotransmitter-identified subpopulations of visceral sensory neurons were also studied. In all three ganglia, calcitonin gene-related peptide (CGRP)-ir was present in many NADPH-diaphorase positive neurons, a subset of which also contained calbindin D-28k-ir. In the nodose ganglion, many (42%) of tyrosine hydroxylase (TH)-ir neurons also contained NADPH diaphorase activity but did not contain calbindin D-28k-ir. These data are consistent with a potential co-operative role for calbindin D-28k and NADPH-diaphorase in the functions of a subpopulation of vagal and glossopharyngeal sensory neurons.
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PMID:Coexistence of calbindin D-28k and NADPH-diaphorase in vagal and glossopharyngeal sensory neurons of the rat. 891 73

Tissue injury initiates a temporally ordered sequence of local cellular and metabolic responses presumably necessary for successful repair. Previous investigations demonstrated that metabolic evidence for nitric oxide synthase (NOS) activity is detectable in wounds only during the initial 48 to 72 hours of the repair process. Present results identify the cell types contributing inducible NOS (iNOS) to experimental wounds in rats. iNOS antigen was expressed in most macrophages present in wounds 6 to 24 hours after injury, and these cells exhibited NAPDH diaphorase and NOS activity. Polymorphonuclear leukocytes contained little iNOS antigen and no NADPH diaphorase activity and were minimally able to convert L-arginine to L-citrulline. The frequency of iNOS-positive macrophages declined on days 3 and 5 after wounding. By day 10, most macrophages in the wound were negative for iNOS. These cells, however, acquired iNOS antigen and activity in culture. Wound fluids, but not normal rat serum, suppressed the induction of iNOS during culture. Findings indicate that the expression of iNOS in healing wounds is restricted to macrophages present during the early phases of repair and that components of wound fluid suppress the induction of iNOS in macrophages in late wounds. Polymorphonuclear leukocytes contribute little iNOS activity to the healing wound.
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PMID:Molecular and metabolic evidence for the restricted expression of inducible nitric oxide synthase in healing wounds. 1023 48

To study the role of nitric oxide synthase (NOS) in rat experimental bronchial asthma. 3H-arginine/3H-L-citrulline conversion technique was used to assay NOS activity of rat lung tissue and histochemical staining method for detect NADPH-d diaphorase. The results revealed that there were significant increase in the level of iNOS activity in asthma group from 152.39% to 249.40%, but the cNOS activity reduced from 64.84% to 61.81% (P < 0.05-0.01). Histochemical staining of NADPH-d showed deep staining of trachial and bronchial epithelium in asthma group. These results suggested that NOS plays a role in regulating airway inflammation and bronchial responsiveness. cNOS possesses a down regulatory effect, while iNOS upregulatory. The occurrence of airway inflammation is earlier than that of smooth muscle contraction and endothelial injury.
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PMID:[An experimental study on the effect of nitric oxide synthase in bronchial asthma]. 1043 84

Experiments were performed to test the hypothesis that diabetes mellitus disrupts the balance between synthesis and degradation of nitric oxide (NO) in the renal cortex. Diabetes was induced by injection of streptozotocin, and sufficient insulin was provided to maintain moderate hyperglycemia for the ensuing 2 wk. Despite an 80% increase in total NO synthase activity measured by L-citrulline assay, nicotinamide adenine dinucleotide phosphate-diaphorase staining was unaltered, and no changes in NO synthase isoform protein levels or their distribution were evident in renal cortex from diabetic rats. Superoxide anion production was accelerated twofold in renal cortical slices from diabetic rats, with an associated 50% increase in superoxide dismutase activity. Western blots prepared by use of a monoclonal antinitrotyrosine antibody revealed an approximately 70-kD protein in renal cortex from sham rats, the nitrotyrosine content of which was threefold greater in cortical samples from diabetic rats. These observations indicate that the early stage of diabetes mellitus provokes accelerated renal cortical superoxide anion production in a setting of normal or increased NO production. This situation can be expected to promote peroxynitrite formation, resulting in the tyrosine nitration of a single protein of unknown identity, as well as a decline in the bioavailability of NO. These events are consistent with the postulate that oxidative stress promotes NO degradation in the renal cortex during the early stage of diabetes mellitus.
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PMID:Nitric oxide synthesis and oxidative stress in the renal cortex of rats with diabetes mellitus. 1146 35

Since the interneuronal messenger nitric oxide (NO) can not be stored in neurones, the regulation of the NO-producing enzyme nitric oxide synthase (NOS) is crucial. Neuronal NOS metabolises L-arginine to nitric oxide (NO) and L-citrulline in a Ca(2+)-dependent manner. Thus, availability of L-arginine to NOS may modulate NO production. In this study, we examined the cellular distribution of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase, L-arginine and L-citrulline. Using NADPH-diaphorase histochemistry to visualise putative NO-producing cells and immunocytochemistry to localise L-arginine, we showed that the distribution of L-arginine-immunoreactive neurones correlates well with those of NADPH-diaphorase-positive neurones in cerebral ganglia of the pulmonate Helix pomatia. However, substrate and enzyme were visualised in separate but adjacent neurones. We further examined whether NADPH-diaphorase-labelled cells contain the L-citrulline. Following elevation of intracellular Ca(2+) by the Ca(2+) ionophore, ionomycin, or by a high-K(+) solution, the number of L-citrulline-immunoreactive neurones in mesocerebrum and pedal lobe increased up to tenfold. Preincubation of ganglia with the NOS inhibitor N(G)-nitro-L-arginine prevented ionomycin or high-K(+) solution-induced L-citrulline synthesis. Most L-citrulline-immunoreactive neurones contain NADPH-diaphorase activity. In conclusion, these experiments indicate a complementary distribution of NOS and L-arginine and suggest an unknown signalling pathway between neurones to maintain L-arginine and NO homeostasis.
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PMID:Complementary distribution of NADPH-diaphorase and l-arginine in the snail nervous system. 1190 76


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