The stimulatory effects of Hofmeister ions on the activities of neuronal nitric-oxide synthase. Apparent substrate inhibition by l-arginine is overcome in the presence of protein-destabilizing agents.
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A variety of monovalent anions and cations were effective in stimulating both calcium ion/calmodulin (Ca2+/CaM)-independent NADPH-cytochrome c reductase activity of, and Ca2+/CaM-dependent nitric oxide (NO.) synthesis by, neuronal nitric oxide synthase (nNOS). The efficacy of the ions in stimulating both activities could be correlated, in general, with their efficacy in precipitating or stabilizing certain proteins, an order referred to as the Hofmeister ion series. In the hemoglobin capture assay, used for measurement of NO. production, apparent substrate inhibition by L-arginine was almost completely reversed by the addition of sodium perchlorate (NaClO4), one of the more effective protein-destabilizing agents tested. Examination of this phenomenon by the assay of L-arginine conversion to L-citrulline revealed that the stimulatory effect of NaClO4 on the reaction was observed only in the presence of oxyhemoglobin or superoxide anion (generated by xanthine and xanthine oxidase), both scavengers of NO. Spectrophotometric examination of nNOS revealed that the addition of NaClO4 and a superoxide-generating system, but neither alone, prevented the increase of heme absorption at 436 nm, which has been attributed to the nitrosyl complex. The data are consistent with the release of autoinhibitory NO. coordinated to the prosthetic group of nNOS, which, in conjunction with an NO. scavenger, causes stimulation of the reaction. (+info)
Production of anti-peptide antibody of rat brain nitric-oxide synthase.
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AIM: To raise antibody of rat brain nitric-oxide synthase (bNOS) through immunizing animal with a peptide of bNOS that can represent the holoprotein. METHODS: The amino acid sequence for the bNOS was analyzed by GenePro computer program. According to the hydrophilicity, hydrophobicity, antigenicity, and the potentiality to form protein second structures of alpha-helix, beta-sheet and beta-turn, the structure of bNOS was predicted. The peptide 277-287 was selected that was predicted to be in the antigen epitope of bNOS. The peptide was chemically synthesized, coupled to keyhole limphet hemocyanin carrier protein and injected into rabbits to raise antibody. The specificity of the antibody was tested by enzyme-linked immunosorbent assay, immunohistochemistry, and Western blotting. RESULTS: The antibody bound the protein in rat cerebellum extract. In Western blotting, the antibody bound the protein band of 150 kDa in SDS-PAGE, and the binding was inhibited by peptide conjugated with carrier protein. In immunohistochemistry, the stain was collocated with the stain in NADPH-dehydrogenase histochemistry. CONCLUSION: The antibody against the peptide recognized the natural bNOS in rat brain, and the peptide 277-287 was located on the surface of bNOS. (+info)
Modulation of the remote heme site geometry of recombinant mouse neuronal nitric-oxide synthase by the N-terminal hook region.
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The role of two essential residues at the N-terminal hook region of neuronal nitric-oxide synthase (nNOS) in nitric-oxide synthase activity was investigated. Full-length mouse nNOS proteins containing single-point mutations of Thr-315 and Asp-314 to alanine were produced in the Escherichia coli and baculovirus-insect cell expression systems. The molecular properties of the mutant proteins were analyzed in detail by biochemical, optical, and electron paramagnetic resonance spectroscopic techniques and compared with those of the wild-type enzyme. Replacement of Asp-314 by Ala altered the geometry around the heme site and the substrate-binding pocket of the heme domain and abrogated the ability of nNOS to form catalytically active dimers. Replacement of Thr-315 by Ala reduced the protein stability and altered the geometry around the heme site, especially in the absence of bound (6R)-5,6,7, 8-tetrahydro-L-biopterin cofactor. These results suggest that Asp-314 and Thr-315 both play critical structural roles in stabilizing the heme domain and subunit interactions in mouse nNOS. (+info)
Mechanism of superoxide generation by neuronal nitric-oxide synthase.
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Neuronal nitric-oxide synthase (NOS I) in the absence of L-arginine has previously been shown to generate superoxide (O-2) (Pou, S., Pou, W. S., Bredt, D. S., Snyder, S. H., and Rosen, G. M. (1992) J. Biol. Chem. 267, 24173-24176). In the presence of L-arginine, NOS I produces nitric oxide (NO.). Yet the competition between O2 and L-arginine for electrons, and by implication formation of O-2, has until recently remained undefined. Herein, we investigated this relationship, observing O-2 generation even at saturating levels of L-arginine. Of interest was the finding that the frequently used NOS inhibitor NG-monomethyl L-arginine enhanced O-2 production in the presence of L-arginine because this antagonist attenuated NO. formation. Whereas diphenyliodonium chloride inhibited O-2, blockers of heme such as NaCN, 1-phenylimidazole, and imidazole likewise prevented the formation of O-2 at concentrations that inhibited NO. formation from L-arginine. Taken together these data demonstrate that NOS I generates O-2 and the formation of this free radical occurs at the heme domain. (+info)
The contribution of various NOS gene products to HIV-1 coat protein (gp120)-mediated retinal ganglion cell injury.
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PURPOSE: There is growing evidence that the neuronal pathology seen with HIV-1 is mediated, at least in part, through an excitotoxic/free radical pathway. Nitric oxide (NO) plays a critical role in the nervous system, in both normal and pathologic states, and appears to be involved in a variety of excitotoxic pathways. Whether isoforms of nitric oxide synthase (NOS) are involved in gp120-mediated neuronal loss in the retina was therefore explored. METHODS: To determine which (if any) of the various isoforms of NOS are critical in gp120-mediated damage in the retina, neuronal NOS-deficient [nNOS(-/-)], endothelial NOS-deficient [eNOS(-/ -)], and immunologic NOS-deficient [iNOS(-/-)] mice were subjected to intravitreal injections of gp120. RESULTS: Retinal ganglion cells in the nNOS(-/-) mouse were relatively resistant to gp120, manifesting attenuation of gp120-induced injury compared with wild-type mice. The iNOS(-/-) and eNOS(-/-) mice were as susceptible to gp120 toxicity as control animals. NOS inhibitors were protective against this toxicity. CONCLUSIONS: The presence of nNOS is a prerequisite for the full expression of gp120-mediated loss in the retina; eNOS and iNOS do not appear to play a significant role. (+info)
Rapid inactivation of NOS-I by lipopolysaccharide plus interferon-gamma-induced tyrosine phosphorylation.
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Human astrocytoma T67 cells constitutively express a neuronal NO synthase (NOS-I) and, following administration of lipopolysaccharide (LPS) plus interferon-gamma (IFNgamma), an inducible NOS isoform (NOS-II). Previous results indicated that a treatment of T67 cells with the combination of LPS plus IFNgamma, by affecting NOS-I activity, also inhibited NO production in a very short time. Here, we report that under basal conditions, a NOS-I protein of about 150 kDa was weakly and partially tyrosine-phosphorylated, as verified by immunoprecipitation and Western blotting. Furthermore, LPS plus IFNgamma increased the tyrosine phosphorylation of NOS-I, with a concomitant inhibition of its enzyme activity. The same effect was observed in the presence of vanadate, an inhibitor of phosphotyrosine-specific phosphatases. On the contrary, genistein, an inhibitor of protein-tyrosine kinases, reduced tyrosine phosphorylation of NOS-I, enhancing its enzyme activity. Finally, using reverse transcriptase-polymerase chain reaction, we have observed that a suboptimal induction of NOS-II mRNA expression in T67 cells was enhanced by vanadate (or L-NAME) and inhibited by genistein. Because exogenous NO has been found to suppress NOS-II expression, the decrease of NO production that we have obtained from the inactivation of NOS-I by LPS/IFNgamma-induced tyrosine phosphorylation provides the best conditions for NOS-II expression in human astrocytoma T67 cells. (+info)
Interaction of neuronal nitric-oxide synthase and phosphofructokinase-M.
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Neurons that express neuronal nitric-oxide synthase (nNOS) are resistant to NO-induced neurotoxicity; however, the mechanism by which these neurons are protected is not clear. To identify proteins possibly involved in this process, we performed affinity chromatography with the nNOS PDZ domain, a N-terminal motif that mediates protein interactions. Using this method to fractionate soluble tissue extracts, we identified the muscle isoform of phosphofructokinase (PFK-M) as a protein that binds to nNOS both in brain and skeletal muscle. PFK-M interacts with the PDZ domain of nNOS, and nNOS-PFK-M binding can be competed by peptides that bind to the PDZ domain of nNOS. We found that nNOS is significantly associated with PFK-M in skeletal muscle because nNOS can be immunodepleted from cytosolic skeletal muscle extracts using an antibody directed against PFK-M. In brain, nNOS and PFK-M are both enriched in synaptosomes, and specifically, in the synaptic vesicle fraction, where they can interact. At the cellular level, PFK-M is enriched in neurons that express nNOS protein. As fructose-1, 6-bisphosphate, the product of PFK activity, is neuroprotective, the interaction of nNOS and PFK may contribute to neuroprotection of nNOS positive cells. (+info)
Inhibition of inducible nitric oxide synthase by beta-lapachone in rat alveolar macrophages and aorta.
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Beta-lapachone, a plant product, has been shown to be a novel inhibitor of DNA topoisomerase. In this study, we performed experiments to examine the effects of beta-lapachone on lipopolysaccharide (LPS)-induced inducible nitric oxide (NO) synthase (iNOS) in rat alveolar macrophages and aortic rings. In alveolar macrophages, incubation with LPS (10 microg ml(-1)) for various time intervals resulted in a significant increase in nitrite production and iNOS protein synthesis, that was inhibited by coincubation with beta-lapachone (1-4.5 microM) without any cytotoxic effects. However, addition of beta-lapachone after induction of NO synthase by LPS failed to affect the nitrite production. Treatment with LPS (10 microg ml(-1)) for 6 h resulted in significant expression of mRNA for iNOS which was significantly inhibited in the presence of beta-lapachone (3 microM) in alveolar macrophages. In endothelium-intact rings of thoracic aorta, beta-lapachone (1 and 3 microM) markedly inhibited the hypocontractility to phenylephrine in aortic rings treated with LPS (10 microg ml(-1)) for 4 h. When beta-lapachone was added 3 h after LPS into the medium, the contractions evoked by phenylephrine were not significantly different in the presence or absence of beta-lapachone. Treatment with LPS (10 microg ml(-1)) for 4 h resulted in a significant increase in iNOS protein synthesis which was inhibited in the presence of beta-lapachone (3 microM), but did not affect the constitutive (endothelial and neuronal) NOS forms in aortic rings. These results indicate that beta-lapachone is capable of inhibiting expression and function of iNOS in rat alveolar macrophages and aortic rings. It is considered that beta-lapachone can be developed as a potential anti-inflammatory agent in the future. (+info)