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The Modification of Cysteine
Published in Roger L. Lundblad, Chemical Reagents for Protein Modification, 2020
Cysteine is relatively sensitive to oxidation but there is little selectivity in these reactions. Mild oxidizing conditions can result in the formation of disulfide bonds with appropriately aligned cysteinyl residues. Formation of sulfenic acid is generally readily reversible unless stabilized by local conditions3 and more highly oxidized forms such as cysteine-sulfonic acid are more frequently observed. More rigorous conditions such as treatment with performic acid result in the formation of cysteic acid.
Isolation and Characterization of Pregnancy-Related Proteins
Published in Gábor N. Than, Hans Bohn, Dénes G. Szabó, Advances in Pregnancy-Related Protein Research, 2020
The amino acid analysis was carried out by the method of Moore et al.11 using a Multichrome B liquid chromatograph supplied by Beckman. Cystine was determined as cysteic acid after oxidation of the protein with performic acid.12 The tryptophan content was determined directly by the photometric method of Edelhoch.13 These methods have been used to determine the amino acid compositions of the pregnancy proteins SP1 to SP3 and of the soluble placental tissue proteins PP1 and PP4 through PP21, but the results of these analyses are not reported here.
Reactivities of Amino Acids and Proteins with Iodine
Published in Erwin Regoeczi, Iodine-Labeled Plasma Proteins, 2019
A small amount of H2SO4 also forms during the reaction. Ramachandran27 mentions that he has identified cysteic acid in hydrolysates of iodinated casein. Unfortunately, the original work underlying this statement is not readily available, and hence no review of the experimental conditions can be given here. Nevertheless, cystine oxidation by iodine may be compared to an “endurance test”, for even under optimal conditions (i.e., using nonprotein cystine), the reaction is extremely slow, lasting over a week.26 Not surprisingly, therefore, Koshland and colleagues28 found only traces of cysteic acid in acid hydrolysates of rabbit IgG that was iodinated to saturation by using ICI (at which point 100 atoms of I were incorporated per molecule of immunoglobulin).
Interactions of 2,6-substituted purines with purine nucleoside phosphorylase from Helicobacter pylori in solution and in the crystal, and the effects of these compounds on cell cultures of this bacterium
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Marta Narczyk, Marta Ilona Wojtyś, Ivana Leščić Ašler, Biserka Žinić, Marija Luić, Elżbieta Katarzyna Jagusztyn-Krynicka, Zoran Štefanić, Agnieszka Bzowska
Two other purines, 6BnS-Pu and 2,6-diCl-Pu, the former lacking chlorine atoms and the latter lacking the benzyl substituent, bind with a purine ring flipped around with respect to the two previous structures (Figure 8). The electron density of the phenyl arm in the structure of 6BnS-Pu is very poorly visible due to its large conformational mobility. Positions of Tris and PO4 molecules are the same as in the structures with 6BnS-2Cl-Pu and 6BnO-2Cl-Pu. 2,6-diCl-Pu, which contains two Cl atoms, is very well defined in all twelve open active sites (chain A is shown in Figure 8). In the pentose binding part, one molecule of imidazole is visible and in the place of PO4, there is one Mg ion coordinated by water molecules and by Arg43. In all active sites, Cys19 is oxidised to cysteic acid (OCS) visible to the far right (Figure 8(D)).
A patent review of myeloperoxidase inhibitors for treating chronic inflammatory syndromes (focus on cardiovascular diseases, 2013-2019)
Published in Expert Opinion on Therapeutic Patents, 2020
Jalal Soubhye, Pierre Van Antwerpen, François Dufrasne
During inflammation, MPO can be released outside the neutrophils causing oxidative damages for the host tissues [5]. These damages can be caused by two processes: 1) producing HOCl which oxidizes the biomacromolecules such as DNA, RNA, proteins, lipoproteins [15]; 2) direct oxidation by MPO of which some amino acids and hormones can be substrates (ex: tyrosine and serotonin) [16]. HOCl produced by MPO is able to oxidize a large variety of biomolecules by chlorination and/or oxidation [17]. It oxidizes sulfhydryl groups in proteins causing their inactivation. This oxidation can form disulfide bonds that can result in the crosslinking of proteins. However, oxidation of Cys by HOCl gives cysteic acid and cysteine [18]. Hypochlorous acid can readily react with the amino acids which have an amine side chain (ex. Lys) resulting in a chloramine compound. Tyr can be oxidized by MPO giving either o,o’-dityrosine (di-tyr) via direct oxidation or chlorotyrosine (Cl-tyr) via HOCl where Cl−tyr is considered as the marker of MPO oxidation [19]. HOCl can attack the free amino acids as well as the residues of amino acids in proteins [17]. In addition, the nitrogen atoms of nucleosides are readily oxidized by HOCl causing damages in DNA and RNA [20]. Reactions of unsaturated fatty acids and cholesterol with HOCl are also possible that generate lipid hydroperoxide and cholesterol chlorhydrin [21,22].
Xenobiotic C-sulfonate derivatives; metabolites or metabonates?
Published in Xenobiotica, 2018
Sulfoquinovose (6-deoxy-6-sulfo-D-glucopyranose) is a sulfonic acid derivative of glucose present in plants as part of the sulfolipid, sulfoquinovosyldiacylglycerol, an important component of their thylakoid membranes and the site of the light dependent reactions of photosynthesis. Amendments to the previously proposed biosynthetic “sulphoglycolytic” pathway (Benson, 1963; Davies et al., 1966) have suggested that sulfite may be added across the double bond of a modified sugar, UDP-4-ketoglucose-5-ene (Pugh et al., 1995). An enzyme, UDP-sulfoquinovase synthase (EC 3.13.1.1), has been isolated from the small flowering plant, thale cress (Arabidopsis thaliana), that is able to introduce the sulfonate moiety by combining UDP-glucose with sulfite, albeit with a low turnover rate (Sanda et al., 2001). A group of sulfonolipids, known as capnoids, have been isolated from gliding bacteria (Cytophaga spp.), the most extensively studied of which is capnine (2-amino-3-hydroxy-15-methylhexadecane-1-sulfonic acid). This material is formed by the condensation of a fatty acyl CoA with cysteic acid (HO3SCH2CH(NH)CO2H) (Abbanat et al., 1985). Cysteic acid may be formed readily from cysteine by a two-step oxygenation reaction (cysteine → cysteine sulfinic acid → cysteic acid) but radiolabelled cysteine was not incorporated into capnine by these bacteria (White, 1984). As an alternative, it has been suggested that cysteic acid could be formed from sulfite condensing with a suitable organic acceptor and then the sulfur being further oxidized (Chapeville & Fromageot, 1954; Greenberg, 1954; Singer & Kearney, 1955) or even via the use of sulfate (Gilmore et al., 1989). In any event, the sulfonic acid moiety is added as part of the larger cysteic acid molecule and hence capnoid synthesis does not involve a carbon sulfonation reaction.