Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 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

A nitric oxide synthase was partially purified from soluble extracts of Trypanosoma cruzi epimastigote forms. The conversion of L-arginine to citrulline by this enzyme activity required NADPH and was blocked by EGTA. The reaction was activated by Ca2+, calmodulin, tetrahydrobiopterin, and FAD, and inhibited by N omega-methyl-L-arginine. L-Glutamate and N-methyl-D-aspartate stimulated in vivo conversion of L-arginine to citrulline by epimastigote cells. These stimulations could be blocked by EGTA, MK-801, and ketamine and enhanced by glycine. A sodium nitroprusside-activated guanylyl cyclase activity was detected in cell-free, soluble preparations of T. cruzi epimastigotes. L-Glutamate, N-methyl-D-aspartate, and sodium nitroprusside increased epimastigote cyclic GMP levels. MK-801 bound specifically to T. cruzi epimastigote cells. This binding was competed by ketamine and enhanced by glycine or L-serine. Evidence thus indicates that in T. cruzi epimastigotes, L-glutamate controls cyclic GMP levels through a pathway mediated by nitric oxide.
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PMID:The nitric oxide transduction pathway in Trypanosoma cruzi. 754 49

Nitric oxide (NO) was discovered to be a potent vasodilator, inhibitor of platelet aggregation, and active species of nitroglycerin before the discovery of endothelium-derived relaxing factor (EDRF) in 1980. Subsequent studies revealed that EDRF is NO, and is synthesized by mammalian cells from L-arginine through a complex oxidation reaction catalyzed by the flavo-hemoprotein NO synthase (NOS). NOS catalyzes the NADPH- and oxygen-dependent oxygenation of L-arginine to NO plus L-citrulline in a reaction that requires at least six cofactors including NADPH, FAD, FMN, tetrahydrobiopterin, heme, and calmodulin. NO elicits its known physiological actions by activating cytosolic guanylate cyclase, which converts GTP to cyclic GMP. Endothelial NOS and neuronal NOS are constitutively present and activated by increases in intracellular calcium triggered by endogenous chemicals. NO then diffuses into nearby target cells to elevate cyclic GMP levels and thereby trigger cell function. NOS activity can also be regulated by a negative feedback mechanism involving NO itself. Much greater quantities of NO are produced pathophysiologically by a distinct form of NOS that can be induced in vascular endothelium, smooth muscle and macrophages by endotoxin and cytokines. This high-output production of NO is not regulated by calcium and is cytotoxic by mechanisms involving interaction with iron-containing proteins.
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PMID:Physiology and pathophysiology of nitric oxide. 874 1

Nitric oxide, derived from L-arginine by the enzyme nitric oxide synthase, is an activator of the soluble guanylate cyclase and a cellular messenger. This work demonstrates that, in cat brain, the neuronal constitutive nitric oxide synthase activity is a) NADPH/calcium dependent, b) independent upon exogenous calmodulin in crude brain supernatant, c) significantly enhanced by exogenous FAD and tetrahydrobiopterin (Vmax: 118 instead of 59.4 pmol of citrulline formed .mg of prot.-1 min-1, d) inhibited by calcium chelators and calmodulin antagonist, and e) present in several neuroanatomical structures. Moreover, the Km value for L-arginine was of 11 microM instead of 41 microM in the presence of FAD and tetrahydrobiopterin in the incubation mixture, thus demonstrating that these cofactors are able to stabilize the enzyme-substrate interactions.
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PMID:Nitric oxide synthase in cat brain: cofactors--enzyme-substrate interaction. 879 Oct 99

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.
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PMID:Nitric oxide synthase and cGMP activity in the salivary glands of the American dog tick Dermacentor variabilis. 1067 47

The synthesis of the free radical gas nitric oxide (NO) is catalyzed by the enzyme NO synthase (NOS). NOS converts arginine and molecular oxygen to NO and citrulline in a reaction that requires NADPH, FAD, FMN, and tetrahydrobiopterin as cofactors. Three types of NOS have been identified by molecular cloning. The activity of the constitutively expressed neuronal NOS (nNOS) and endothelial NOS (eNOS) is Ca(2+)/calmodulin-dependent, whereas that the inducible NOS (iNOS) is Ca(2+)-insensitive. The predominant NOS isoform in skeletal muscle is nNOS. It is present at the sarcolemma of both extra- and intrafusal muscle fibers. An accentuated accumulation of nNOS is found in the endplate area. This strict sarcolemmal localization of nNOS is due its association with the dystrophin-glycoprotein complex, which is mediated by the syntrophins. The activity of nNOS in skeletal muscle is regulated by developmental, myogenic, and neurogenic influences. NO exerts several distinct effects on various aspects of skeletal muscle function, such as excitation-contraction coupling, mitochondrial energy production, glucose metabolism, and autoregulation of blood flow. Inside the striated muscle fibers, NO interacts directly with several classes of proteins, such as soluble guanylate cyclase, ryanodine receptor, sarcoplasmic reticulum Ca(2+)-ATPase, glyceraldehyde-3-phosphate dehydrogenase, and mitochondrial respiratory chain complexes, as well as radical oxygen species. In addition, NO produced and released by contracting muscle fibers diffuses to nearby arterioles where it acts to inhibit reflex sympathetic vasoconstriction.
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PMID:NO message from muscle. 1174 89

Cyclic nucleotides, cAMP and cGMP, are ubiquitous second messengers that regulate metabolic and behavioral responses in diverse organisms. We describe purification, engineering, and characterization of photoactivated nucleotidyl cyclases that can be used to manipulate cAMP and cGMP levels in vivo. We identified the blaC gene encoding a putative photoactivated adenylyl cyclase in the Beggiatoa sp. PS genome. BlaC contains a BLUF domain involved in blue-light sensing using FAD and a nucleotidyl cyclase domain. The blaC gene was overexpressed in Escherichia coli, and its product was purified. Irradiation of BlaC in vitro resulted in a small red shift in flavin absorbance, typical of BLUF photoreceptors. BlaC had adenylyl cyclase activity that was negligible in the dark and up-regulated by light by 2 orders of magnitude. To convert BlaC into a guanylyl cyclase, we constructed a model of the nucleotidyl cyclase domain and mutagenized several residues predicted to be involved in substrate binding. One triple mutant, designated BlgC, was found to have photoactivated guanylyl cyclase in vitro. Irradiation with blue light of the E. coli cya mutant expressing BlaC or BlgC resulted in the significant increases in cAMP or cGMP synthesis, respectively. BlaC, but not BlgC, restored cAMP-dependent growth of the mutant in the presence of light. Small protein sizes, negligible activities in the dark, high light-to-dark activation ratios, functionality at broad temperature range and physiological pH, as well as utilization of the naturally occurring flavins as chromophores make BlaC and BlgC attractive for optogenetic applications in various animal and microbial models.
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PMID:Natural and engineered photoactivated nucleotidyl cyclases for optogenetic applications. 2103 May 91