(1/982) Increased oxidative stress in the RAW 264.7 macrophage cell line is partially mediated via the S-nitrosothiol-induced inhibition of glutathione reductase.
We investigated whether endogenously or exogenously produced nitric oxide (NO) can inhibit cellular glutathione reductase (GR) via the formation of S-nitrosothiols to decrease cellular glutathione (GSH) and increase oxidative stress in RAW 264.7 cells. The specificity of this inhibition was demonstrated by addition of a NO-synthase inhibitor, and met- or oxyhemoglobin. Using isolated GR we found that only certain NO donors inhibit this enzyme via S-nitrosothiol. Furthermore, we found that cellular GSH decrease is paralleled by an increase of superoxide anion production. Our results show that the GR enzyme is a potential target of S-nitrosothiols to decrease cellular GSH levels and to induce oxidative stress in macrophages. (+info)
(2/982) Membrane-bound DD-carboxypeptidase and transpeptidase activities from Bacillus megaterium KM at pH 7. General properties, substrate specificity and inhibition by beta-lactam antibiotics.
1. The membranes from Bacillus megaterium KM contained a DD-carboxypeptidase with optimum activity under the following conditions: pH 7; ionic strength, 1.3 M; temperature, 40 degrees C and below 20 degrees C. It did not require any divalent cation, but was inactivated by Cu2+ and Hg2+. It was stimulated by 2-mercaptoethanol and low concentrations of p-chloromercuribenzoate. 2. The membrane preparation also catalyzed a simple transpeptidation reaction using as carboxyl acceptors D-alanine or glycine. 3. The conditions for optimum activity, temperature-inactivation, temperature-dependence of the activity, carboxyl donor specificity, sensitivity to beta-lactam antibiotics, and insensitivity to potential peptide inhibitors of both enzyme activities, was identical. The DD-carboxypeptidase showed inhibition by D-alanine and Ac2-L-Lys-D-Ala. 4. The inhibition by beta-lactam antibiotic was reversible for both enzymic activities and the time-dependence for their recovery was identical. 5. The DD-carboxypeptidase was very sensitive to changes in the configuration and size of the side-chains of the C-terminal dipeptide of the substrate. Amino acid residues at the C-terminus that precluded the peptide from being a DD-carboxypeptidase substrate were not acceptors in the transpeptidation reaction. Dipeptides were not acceptors for the 'model transpeptidase'. 6. It is suggested that both activities are catalysed by the same enzyme molecule, whose physiological role is not the formation of peptide crosslinks during peptidoglycan biosynthesis. (+info)
(3/982) Fas-induced caspase denitrosylation.
Only a few intracellular S-nitrosylated proteins have been identified, and it is unknown if protein S-nitrosylation/denitrosylation is a component of signal transduction cascades. Caspase-3 zymogens were found to be S-nitrosylated on their catalytic-site cysteine in unstimulated human cell lines and denitrosylated upon activation of the Fas apoptotic pathway. Decreased caspase-3 S-nitrosylation was associated with an increase in intracellular caspase activity. Fas therefore activates caspase-3 not only by inducing the cleavage of the caspase zymogen to its active subunits, but also by stimulating the denitrosylation of its active-site thiol. Protein S-nitrosylation/denitrosylation can thus serve as a regulatory process in signal transduction pathways. (+info)
(4/982) Redox modulation of intracellular free calcium concentration in thyroid FRTL-5 cells: evidence for an enhanced extrusion of calcium.
Redox modulation is involved in the regulation of the intracellular free calcium concentration ([Ca2+]i) in several cell types. In thyroid cells, including thyroid FRTL-5 cells, changes in [Ca2+]i regulate important functions. In the present study we investigated the effects of the oxidizing compounds thimerosal and t-butyl hydroperoxide on [Ca2+]i in thyroid FRTL-5 cells. Thimerosal mobilized sequestered calcium, and evoked modest store-dependent calcium entry. Both compounds potently attenuated the increase in [Ca2+]i when store-operated calcium entry was evoked with thapsigargin. The entry of barium was not attenuated. Experiments performed with high extracellular pH, in sodium-free buffer and in the presence of vanadate suggested that thimerosal decreased [Ca2+]i by activating a calcium extrusion mechanism, probably a plasma membrane Ca2+-ATPase. All the observed effects were abrogated by the reducing agent beta-mercaptoethanol. The mechanism of action was apparently mediated via activation of protein kinase C, as thimerosal potently stimulated binding of [3H]phorbol 12, 13-dibutyrate, and was without effect on store-operated calcium entry in cells treated with staurosporine or in cells with down-regulated protein kinase C. Thimerosal did not depolarize the membrane potential, as evaluated using patch-clamp in the whole-cell mode. In immunoprecipitates obtained with an antibody against plasma membrane Ca2+-ATPase, we observed several phosphorylated bands in cells stimulated with thimerosal. In conclusion, we have shown that thimerosal attenuates an increase in [Ca2+]i, probably by activating a plasma membrane Ca2+-ATPase. (+info)
(5/982) Hematopoietic growth factors signal through the formation of reactive oxygen species.
Hematopoietic growth factors (HGFs) stimulate growth, differentiation, and prevent apoptosis of progenitor cells. Each growth factor has a specific cell surface receptor, which activates both unique and shared signal transduction pathways. We found that several HGFs, including granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), steel factor (SF), and thrombopoietin (TPO) induce a rapid increase in reactive oxygen species (ROS) in quiescent cells. In an effort to understand the potential biochemical and biological consequences of increased ROS in these cells, we exposed growth factor-deprived cells to hydrogen peroxide (H2O2) at concentrations that increased intracellular ROS. H2O2 induced a dose-dependent increase in tyrosine phosphorylation, including increased tyrosine phosphorylation of the GM-CSF receptor beta chain (betac), STAT5, and other signaling proteins. H2O2 also induced expression of the early response gene c-FOS, and G1- to S-phase transition, but not S- to G2/M-phase transition of MO7e cells. The cell permeable antioxidant pyrrolidine dithiocarbamate (PDTC) decreased the intracellular levels of ROS and inhibited tyrosine phosphorylation induced by GM-CSF in MO7e cells, suggesting that ROS generation plays an important role in GM-CSF signaling. Consistent with this notion, PDTC and two other antioxidants, N-acetyl cysteine and 2-mercaptoethanol, reduced growth and viability of MO7e cells. These results suggest that generation of ROS in response to HGFs may contribute to downstream signaling events, especially those involving tyrosine phosphorylation. (+info)
(6/982) The microsporidian spore invasion tube. The ultrastructure, isolation, and characterization of the protein comprising the tube.
The extrusion apparatus of the microsporidian parasitic protozoan Nosema michaelis discharges an invasion (or polar) tube with a velocity suitalbe for piercing cells and injecting infective sporoplasm. The tube is composed of a polar tube protein (PTP) which consists of a single, low molecular weight polypeptide slightly smaller than chymotrypsinogen-A. Assembled PTP tubes resist dissociation in sodium dodecyl sulfate and brief exposures in media at extreme ends of the pH range; however, the tubes are reduced by mercaptoethanol and dithiothreitol. When acidified, mercaptoethanol-reduced PTP self-assembles into plastic, two-dimensional monolayers. Dithiothreitol-reduced PTP will not reassemble when acidified. Evidence is presented which indicates that PTP is assembled as a tube within the spore; that the ejected tube has plasticity during sporoplasm passage; and, finally, that the subunits within the tube polymer are bound together, in part, by interprotein disulfide linkages. (+info)
(7/982) Intraprotein electron transfer between tyrosine and tryptophan in DNA photolyase from Anacystis nidulans.
Light-induced electron transfer reactions leading to the fully reduced, catalytically competent state of the flavin adenine dinucleotide (FAD) cofactor have been studied by flash absorption spectroscopy in DNA photolyase from Anacystis nidulans. The protein, overproduced in Escherichia coli, was devoid of the antenna cofactor, and the FAD chromophore was present in the semireduced form, FADH., which is inactive for DNA repair. We show that after selective excitation of FADH. by a 7-ns laser flash, fully reduced FAD (FADH-) is formed in less than 500 ns by electron abstraction from a tryptophan residue. Subsequently, a tyrosine residue is oxidized by the tryptophanyl radical with t(1)/(2) = 50 microseconds. The amino acid radicals were identified by their characteristic absorption spectra, with maxima at 520 nm for Trp. and 410 nm for TyrO. The newly discovered electron transfer between tyrosine and tryptophan occurred for approximately 40% of the tryptophanyl radicals, whereas 60% decayed by charge recombination with FADH- (t(1)/(2) = 1 ms). The tyrosyl radical can also recombine with FADH- but at a much slower rate (t(1)/(2) = 76 ms) than Trp. In the presence of an external electron donor, however, TyrO. is rereduced efficiently in a bimolecular reaction that leaves FAD in the fully reduced state FADH-. These results show that electron transfer from tyrosine to Trp. is an essential step in the process leading to the active form of photolyase. They provide direct evidence that electron transfer between tyrosine and tryptophan occurs in a native biological reaction. (+info)
(8/982) Relationships between nitric oxide, nitroxyl ion, nitrosonium cation and peroxynitrite.
This review is concerned mainly with the three redox-related, but chemically distinct, species NO-, NO. and NO+, with greatest emphasis being placed on the chemistry and biology of the nitroxyl ion. Biochemical routes for the formation of nitroxyl ion and methods for showing the intermediacy of this species are discussed, together with chemical methods for generating nitroxyl ion in solution. Reactions of nitroxyl ion with NO., thiols, iron centres in haem and with dioxygen are reviewed The significance of the reaction between NO- and dioxygen as a source of peroxynitrite is assessed, and attention drawn to the possible significance of the spin state of the nitroxyl ion in this context. The biological significance of nitrosation and the importance of S-nitrosothiols and certain metal nitrosyl complexes as carriers of NO+ at physiological pH is stressed. Some features in the chemistry of peroxynitrite are noted. (+info)