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[en] Five different histidine and aspartic acid based tetrapeptides were designed using LOMETS and PyMol. They were chemically synthesized following the solid phase Fmoc-peptide synthesis protocols and were analysed using the reverse-phase High Performance Liquid Chromatography (HPLC) C18 analytical column for the purity. The peptides were further analysed by Liquid Chromatography Mass Spectrometry (LCMS) to see if the desired peptides were synthesized systematically. Copper (II) acetate monohydrate was bound to the peptides and the best molar ratio for the binding of these metal salts to peptides was 2:1. These observations were monitored through several spectroscopic techniques. The first physical observations for the successful synthesis of metallopeptides were the colour change, the melting/ decomposition points and the solubility of these metallopeptides. Due to the visible colour change of the peptides to metallopeptides, UV-Visible spectroscopy and UV-Fluorescence spectroscopy were used as a qualitative analysis tests and the results were in agreement with other researcherss data from similar researches. (author)
[en] We have developed a stereoselective route to isotopically labeled L-aspartic acid using L-serine as a chiral precursor. Labeled serine, prepared biosynthetically was N-protected by conversion to the N-t-Boc derivative. (N-t-Boc)-[3-13C]Serine is cyclized to its β-lactone which was treated with potassium [13C]cyanide to yield L-β-[3,4-13C2]cyanoalanine. Hydrolysis of the cyanoalanine yielded L-[3,4-13C2]aspartic acid. Similarly, L-[4-13C]aspartate was produced from L-serine and K13CN. Using this route, the L-enantiomer was produced in 96% excess. (Author)
[en] Voltage-gated sodium channels are the primary target of pyrethroids, an important class of synthetic insecticides. Pyrethroids bind to a distinct receptor site on sodium channels and prolong the open state by inhibiting channel deactivation and inactivation. Recent studies have begun to reveal sodium channel residues important for pyrethroid binding. However, how pyrethroid binding leads to inhibition of sodium channel deactivation and inactivation remains elusive. In this study, we show that a negatively charged aspartic acid residue at position 802 (D802) located in the extracellular end of transmembrane segment 1 of domain II (IIS1) is critical for both the action of pyrethroids and the voltage dependence of channel activation. Charge-reversing or -neutralizing substitutions (K, G, or A) of D802 shifted the voltage dependence of activation in the depolarizing direction and reduced channel sensitivity to deltamethrin, a pyrethroid insecticide. The charge-reversing mutation D802K also accelerated open-state deactivation, which may have counteracted the inhibition of sodium channel deactivation by deltamethrin. In contrast, the D802G substitution slowed open-state deactivation, suggesting an additional mechanism for neutralizing the action of deltamethrin. Importantly, Schild analysis showed that D802 is not involved in pyrethroid binding. Thus, we have identified a sodium channel residue that is critical for regulating the action of pyrethroids on the sodium channel without affecting the receptor site of pyrethroids.
[en] To determine the efficacy of L-ornithine-L-aspartate in treatment of hepatic encephalopathy. Cirrhotic patients with hyperammonemia and overt hepatic encephalopathy were enrolled. Eighty patients were randomized to two treatment groups, L-ornithine-L-aspartate (20g/d) or placebo, both dissolved in 250mL of 5% dextrose water and infused intravenously for four hours a day for five consecutive days with 0.5 g/kg dietary protein intake at the end of daily treatment period. Outcome variables were postprandial blood ammonia and mental state grade. Adverse reactions and mortality were also determined. Both treatment groups were comparable regarding age, gender, etiology of cirrhosis, Child-Pugh class, mental state grade and blood ammonia at baseline. Although, improvement occurred in both groups, there was a greater improvement in L-ornithine-L-aspartate group with regard to both variables. Four patients in the placebo group and 2 in L-ornithine-L-aspartate group died. L-ornithine-L-aspartate infusions were found to be effective in cirrhotic patients with hepatic encephalopathy. (author)
[en] The multidrug resistant associated protein 1 (or MRP1, ABCC1) encodes two cytoplasmic linker domains (L0 and L1) composed of highly charged sequences with multiple protein kinase A/C phosphorylation sites. In this report we made use of the scanning peptide approach to identify MRP1 linker L1 (L1MRP1) interacting proteins. Scanning heptapeptides covering L1MRP1 126 amino acids (Ile846- Leu972) were synthesized and used in pull-down assays to isolate proteins from cell extracts (human multidrug resistant SCLC cell line; H69/AR). The results show four high affinity binding sequences in L1MRP1 domain [866FLRTYAST867; 906SAGKQLQRQLSSS912; 925ISRHHNSTA927 and 954AQTGQVKLSVYW959] that bound ∼55 kDa and 110 kDa polypeptides. The latter polypeptides were identified by mass spectrometry as α- and β-tubulin monomers and dimers. Western blotting with monoclonal antibodies to α- and β-tubulin proteins confirmed the mass-spectrometry results. Moreover, using recombinant full-length GST-Linker 1 fusion polypeptide (GST-L1MRP1), we confirmed the peptide scanning approach demonstrating specific binding of tubulin to GST-L1MRP1. Intriguingly, substitutions of serine residues in L1MRP1 by aspartic acid, but not alanine, abolished its binding to tubulin, suggesting that phosphorylation of Ser871, 915, 930, and 961 within L1MRP1 may modulate its binding to tubulin. Taken together, the results of this study suggest possible interaction between MRP1 and tubulin that is modulated by phosphorylation of specific sequences in the L1MRP1 domain. - Highlights: • This study shows direct binding between MRP1 Linker 1 (L1MRP1) domain and α- and β-tubulin subunits, using a scanning peptide approach. • Four short and dispersed sequences in L1MRP1 domain interact with α/β-tubulin subunits. • Each sequence in L1MRP1-tubulin binding domain contains predicted protein kinase C/A site. • Substituting 3 of 4 serine with aspartic acid, but not alanine, in L1MRP1 binding domains inhibit their binding to tubulin subunits.
[en] Glassy carbon electrode (GCE) is covalently modified with aspartic acid (Asp). The modified electrode is used for the simultaneous electrochemical determination of hydroquinone (HQ) and catechol (CC) and shows an excellent electrocatalytical effect on the oxidation of HQ and CC by cyclic voltammetry (CV) in 0.1 mol/L acetate buffer solution (pH 4.5). In differential pulse voltammetric (DPV) measurements, the modified electrode could separate the oxidation peak potentials of HQ and CC present in binary mixtures by about 101 mV though the bare electrode gave a single broad response. A successful elimination of the fouling effect by the oxidized product of HQ on the response of CC has been achieved at the modified electrode. The determination limit of HQ in the presence of 0.1 mmol/L CC was 9.0 x 10-7 mol/L and the determination limit of CC in the presence of 0.1 mmol/L HQ was 5.0 x 10-7 mol/L. The proposed method has been applied to the simultaneous determination of HQ and CC in a water sample with simplicity and high selectivity
[en] Three chiral bibenzimidazoles were synthesized by condensation of a-phenylenediamine with L-(+)-glutamic acid, L-(+)-aspartic acid and L-(+)-tariaric acid under microwave irradiation. promoted by polyphosphoric acid (PPA). Compared with the conventional heating methods, tile synthesis of bibenzimidazole compounds under microwave irradiation is rapid, economic and environmentally friendly method, with much higher yield. (author)