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At least 883 records · Page 49Linked to original sources
PubMed2002

Lack of tyrosine nitration by hypochlorous acid in the presence of physiological concentrations of nitrite. Implications for the role of nitryl chloride in tyrosine nitration in vivo.

Elevated levels of reactive nitrogen species (RNS) such as peroxynitrite have been implicated in over 50 diverse human diseases as measured by the formation of the RNS biomarker 3-nitrotyrosine. Recently, an additional RNS was postulated to contribute to 3-nitrotyrosine formation in vivo; nitryl chloride formed from the reaction of nitrite and neutrophil myeloperoxidase-derived hypochlorous acid (HOCl). Whether nitryl chloride nitrates intracellular protein is unknown. Therefore, we exposed intact human HepG2 and SW1353 cells or cell lysates to HOCl and nitrite and examined each for 3-nitrotyrosine formation by: 1) Western blotting, 2) using a commercial 3-nitrotyrosine enzyme-linked immunosorbent assay kit, 3) flow cytometric analysis, and 4) confocal microscopic analysis. With each approach, no significant 3-nitrotyrosine formation was observed in either whole cells or cell lysates. However, substantial 3-nitrotyrosine was observed when peroxynitrite (100 microm) was added to cells or cell lysates. These data suggest that nitryl chloride formed from the reaction of nitrite with HOCl does not contribute to the elevated levels of 3-nitrotyrosine observed in human diseases.

Enzyme-Linked Immunosorbent Assay↗
PubMed1989

Site-specific mutagenesis of lysine-204, tyrosine-224, tyrosine-228, and histidine-307 of porcine kidney D-amino acid oxidase and the implications as to its catalytic function.

In order to evaluate the possible contributions of Lys-204, Tyr-224, Tyr-228, and His-307 in porcine kidney D-amino acid oxidase [EC 1.4.3.3] (DAO) to its catalytic function, we constructed four point mutant cDNAs encoding enzymes possessing Glu-204, Phe-224, Phe-228, and Leu-307 by oligonucleotide-directed in vitro mutagenesis. The four mutant cDNAs and the wild type cDNA could be expressed in vitro with similar efficiencies and about 200 ng of each enzyme protein was produced from 5 micrograms of the respective capped RNA. The electrophoretic mobilities of the in vitro synthesized mutant enzymes on SDS-polyacrylamide gel were almost identical with that of the wild type DAO, and the molecular weight was calculated to be 38,000. The Glu-204 and Phe-224 mutant DAOs showed comparable enzyme activities to that of the wild type enzyme, and were inhibited strongly by sodium benzoate, a potent competitive inhibitor of DAO. The kinetic parameters of the two mutant DAOs were also comparable to those of the wild type DAO. On the other hand, the Phe-228 and Leu-307 mutant DAOs showed no detectable activity. The results indicate that Tyr-228 and His-307 play important roles as to the constitution of the active site or participate in the reaction directly, while Lys-204 and Tyr-224 are not essential in the enzyme reaction.

Animals↗
PubMed1997

The role of the aspartate-arginine-tyrosine triad in the m1 muscarinic receptor: mutations of aspartate 122 and tyrosine 124 decrease receptor expression but do not abolish signaling.

An Asp-Arg-Tyr triad occurs in a majority of rhodopsin-like G protein-coupled receptors. The fully conserved Arg is critical for G protein activation, but the function of the flanking residues is not well understood. We expressed in COS-7 cells m1 muscarinic receptors that were mutated at Asp122 and Tyr124. Most mutations at either position strongly attenuated or prevented the expression of binding sites for the antagonist [3H]N-methylscopolamine. However, sites that were expressed displayed unaltered affinity for the antagonist. Receptor protein, visualized with a carboxyl-terminally directed antibody, was reduced but never completely abolished. The effects of these mutations were partially reversed by the deletion of 129 amino acids from the third intracellular loop of the receptor. In several cases, comparison of immunocytochemistry with binding measurements suggested the presence of substantial amounts of inactive, presumably misfolded, receptor protein. Some of the variants that bound [3H]N-methylscopolamine underwent small changes in their affinities for acetylcholine. All retained nearly normal abilities to mediate an acetylcholine-induced phosphoinositide response. We propose that Asp122 and Tyr124 make intramolecular contacts whose integrity is important for efficient receptor folding but that they do not participate directly in signaling. The role of these residues is completely distinct from that of Arg123, whose mutation abolishes signaling without diminishing receptor expression.

Acetylcholine↗