Reaction Of Cystine Research Articles

Highly cytotoxic bioconjugated gold(I) complexes with cysteine-containing dipeptides.

Several gold(I) complexes with cysteine-containing dipeptides have been prepared starting from cystine by coupling different amino acids and using several orthogonal protections. The first step is the reaction of cystine, where the sulfur centre is protected as disulfide, with Boc2 O in order to protect the amino group, followed by coupling of an amino acid ester; finally the disulfide bridge is broken with mercaptoethanol to afford the dipeptide derivative. Further reaction with [AuCl(PPh3 )] gives the gold-dipeptide-phosphine species. Starting from these formally gold(I) thiolate-dipeptide phosphine complexes with the general formula [Au(SR)(PR3 )] different structural modifications, such as change in the type of the amino protecting group, the type of phosphine, the number of gold(I) atoms per molecule, or the use of a non-proteinogenic conformationally restricted amino acid ester, were introduced in order to evaluate their influence in the biological activity of the final complexes. The cytotoxic activity, in vitro, of these complexes was evaluated against different tumour human cell lines (A549, MiaPaca2 and Jurkat). The complexes show an outstanding cytotoxic activity with IC50 values in the very low micromolar range. Structure-activity relationship studies from the complexes open the possibility of designing more potent and promising gold(I) anticancer agents.

Kinetic and thermodynamic studies on the disulfide-bond reducing potential of hydrogen sulfide

The significance of persulfide species in hydrogen sulfide biology is increasingly recognized. However, the molecular mechanisms of their formation remain largely elusive. The obvious pathway of the reduction of biologically abundant disulfide moieties by sulfide was challenged on both thermodynamic and kinetic grounds. Using DTNB (5,5′-dithiobis-(2-nitrobenzoic acid), also known as Ellman's reagent) as a model disulfide we conducted a comprehensive kinetic study for its reaction with sulfide. The bimolecular reaction is relatively fast with a second-order rate constant of 889 ± 12 M−1s−1 at pH = 7.4. pH dependence of the rate law revealed that the reaction proceeds via the bisulfide anion species with an initial nucleophilic thiol-disulfide exchange reaction to give 5-thio-2-nitrobenzoic acid (TNB) and TNB-persulfide with a pH independent second-order rate constant of 1090 ± 12 M−1s−1. However, kinetic studies and stoichiometric analyses in a wide range of reactant ratios together with kinetic simulations revealed that it is a multistep process that proceeds via kinetically driven, practically irreversible reactions along the disulfide → persulfide → inorganic polysulfides axis. The kinetic model postulated here, which is fully consistent with the experimental data, suggests that the TNB-persulfide is further reduced by sulfide with a second-order rate constant in the range of 5 × 103 – 5 × 104 M−1s−1 at pH 7.4 and eventually yields inorganic polysulfides and TNB. The reactions of cystine and GSSG with sulfide were found to be significantly slower and to occur via more complicated reaction schemes. 1H NMR studies suggest that these reactions also generate Cys-persulfide and inorganic polysulfide species, but in contrast with DTNB, in consecutive equilibrium processes that are sensitive to changes in the reactant and product ratios. Collectively, our results demonstrate that the reaction of disulfides with sulfide is a highly system specific process from both thermodynamic and kinetic aspects, which together with the considerable steady-state concentrations of the reactants in biological systems signifies physiological relevance.

1H NMR of albumin in human blood plasma: drug binding and redox reactions at Cys 34

1H NMR methods are described which allow direct studies of the Cys 34 binding site of albumin in intact human blood plasma in vitro. Antiarthritic gold drugs and the alcohol-aversive drug disulfiram induce a structural transition detectable via Hϵ1 and Hδ2 resonances of His 3 of albumin, and reactions of cystine, glutathione and captopril in plasma have also been investigated. Contrary to most assumptions, little of the albumin in normal plasma appears to be blocked at Cys 34 as a cystine disulfide.

Ac polarography and ac voltammetry of cystine

It has been shown in a recent paper on the reactions of cystine at mercury electrodes [l] that, depending on the potential, cystine undergoes three different kinds of interaction with mercury. First, at the positive limit of polarization, the anodic dissolution of mercury is accelerated by the formation in the solution of mercury cystinate which is subsequently strongly adsorbed at the electrode surface (in the cystinate, mercury is bound to the carboxylic and the amino groups of cystine). Second, in the absence of an applied potential mercury reacts spontaneously with cystine, forming a surface layer of mercuric cysteine thiolate. The potential which mercury thereby acquires lies near the potential of the saturated calomel electrode (SCE) and changes according to the pH of the solution. Finally, in the region around 0.3 V, where cystine is reversibly adsorbed on mercury, a complex equilibrium is established between cystine and mercurous cysteine thiolate. In the present communication we report how the three kinds of interaction can be identified by means of ac techniques. For our measurements we built an apparatus which allows the alternating current in phase with the applied alternating voltage to be distinguished from that out of phase with the voltage [2]. The dropping mercury electrode (DME) and the hanging mercury drop electrode (HMDE) were used as working electrodes for the polarographic and voltammetric studies respectively. The first study of the a.c. polarography of cystine was carried out by Breyer and coworkers [3,4] who used the simple method without phase distinction. They observed two ac peaks; they ascribed the more positive and more prominent peak to the adsorption of cystine and the second peak to a reversible reduction of the adsorbed cystine. Miller [5] and Mairesse-Ducarmois et

The reactions of cystine at mercury electrodes

Cystine in aqueous solutions reacts chemically with mercury, forming the surface-bound cysteine mercuric thiolate. When the potential of mercury is made less positive this compound is transformed (at a partially free mercury surface in a currentless process and at an occupied electrode under the passage of current) into cysteine mercurous thiolate. The latter compound is also formed in a reversible interaction of cystine with mercury in the potential range where cystine is adsorbed. At the negative end of this range the electroreduction of cystine occurs by the reduction of cysteine mercurous thiolate. At negatively charged mercury, where cystine is not adsorbed, two electrons are transferred directly to the cystine SS bond in an overall irreversible process. On the positive side the dissolution of mercury into solutions containing cystine starts by anodic formation of slightly soluble mercuric cystinate near the electrode surface.

Reaction of cystine with tryptophan under the conditions of acid hydrolysis of proteins: Mechanism of action of cystine.

Heating of cystine under the conditions usually used for the HCI-hydrolysis of proteins gave a small amount of bis-(2-amino-2-carboxyethyl) trisulfide (CTS). Tryptophan was greatly degraded by the reaction with CTS under these conditions. This reaction was inhibited by thioglycolic acid or hydroquinone, indicating that it involves a free-radical mechanism. The known reaction of cystine with tryptophan under the same conditions, however, was inhibited by only thioglycolic acid. From these results, it is supposed that sulfenium ion (+SCH2CH(NH2)COOH), not CTS, arising from cystine is mainly responsible for the loss of tryptophan during the acid hydrolysis of proteins.

The reaction of cystine and Alanine-3-sulphinic acid with halogens

Aqueous chlorine and bromine react with cystine, cysteine, alanine-3- sulphinic acid, and cystine S,S-dioxide to give cysteic acid (3) and cysteicylcysteic acid (2).' When the reaction is performed in the presence of other amino acids it is possible to obtain mixed peptides. The mechanism of formation of the peptide bond is discussed and a sulphonic-carboxylic acid mixed anhydride is proposed as an intermediate.

PH dependency of the cyanide-nitroprusside colour reaction of cystine.

Abstract Both the cyanide-nitroprusside colour reaction for cystine and cysteine and the Rothera test for acetone show a marked dependency on the degree of alkalinity of the final reaction mixture. It is recommended that urine specimens for screening by the cyanide-nitroprusside test should first be adjusted to pH 7–8 to ensure satisfactory conditions for colour development.

The Reactivity of Atomic Hydrogen with Cysteine, Cystine, Tryptophan and Tyrosine in Aqueous Solution

AbstractThe reactions of cystine, cysteine, tryptophane and tyrosine in aqueous solution with atomic hydrogen, produced in an electrodeless high frequency discharge, were studied. The specific rate constants for the velocity of the reaction of the substrates with H atoms were found to be ks = 1.5 × 109; 1.0 × 109; 2 × 109 and ∼4 × 1081·mole−1·sec−1 for cystine, cysteine, tryptophan and tyrosine respectively.

Reaction of Cystine with Sodium Sulfide in Sodium Hydroxide Solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReaction of Cystine with Sodium Sulfide in Sodium Hydroxide SolutionG. SATYANARAYANA RAO and GEORGE GORINCite this: J. Org. Chem. 1959, 24, 6, 749–753Publication Date (Print):June 1, 1959Publication History Published online1 May 2002Published inissue 1 June 1959https://doi.org/10.1021/jo01088a005RIGHTS & PERMISSIONSArticle Views929Altmetric-Citations56LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (593 KB) Get e-Alerts Get e-Alerts