Search results for "CYSTEINE"

Spectrophotometric determination of cystine by formation of an o-phthalaldehyde/N-acetyl-l-cysteine derivative

1989

Abstract Cystine reacts with o -phthalaldehyde (OPA) in the absence and presence of a thiol compound to yield different compounds. The use of N -acetyl- l -cysteine as thiol leads to the formation of two derivatives, likely simple and double isoindoles, where the disulfide bond remains unbroken. In contrast, mercaptoethanol gives rise to the reduction of the amino acid to form a cysteine derivative. Obtaining cystine isoindoles makes it possible to spectrophotometrically determine the amino acid after Chromatographic separation and is further evidence of the large stabilization effect produced by N -acetyl- l -cysteine in the formation of OPA-thiol derivatives.

In situ forming hydrogels of new amino hyaluronic acid/benzoyl-cysteine derivatives as potential scaffolds for cartilage regeneration

2012

A new chemical strategy is described to link ethylenediamino (EDA) groups to primary hydroxyl groups of hyaluronic acid (HA) and the obtained derivatives have been characterized by 1H-NMR and 13C-NMR analyses. Such HA–EDA derivatives have been exploited to control the functionalization degree in benzoyl-cysteine (BC) groups, chosen as moieties able to allow both self-assembling in aqueous media and an oxidative crosslinking. In particular, the kinetics of oxidation of thiol groups in HA–EDA–BC derivatives has been studied in Dulbecco's Phosphate Buffer Solution (DPBS) pH 7.4 by colorimetric assays and rheological measurements. Mechanical properties of chemical hydrogels obtained after oxida…

Determining sulfur-containing amino acids by capillary electrophoresis: A fast novel method for total homocyst(e)ine human plasma

1999

A high-performance capillary electrophoresis (HPCE) method based on laser-induced fluorescence detection is presented here. It enables the determination of sulfur-containing amino acids within 15 min. Fluorescence of sulfur-containing amino acids in plasma is linear over a range of 50-150 micromol/L for L-methionine, 5-100 micromol/L for L-homocysteine, and 50-200 micromol/L for L-cysteine. For homocysteine, we were able to detect 1 fmol injected, equivalent to a plasma concentration of 10 nmol/L. A similar sensitivity is present for cysteine, an even lower one being found for methionine. The intra- and interassay relative standard deviations are < 1%. High-performance liquid chromatography…

Differential localization of two acid proteinases in germinating barley (Hordeum vulgare) seed

1995

A cathepsin D-like aspartic proteinase (EC 3.4.23) is abundant in ungerminated barley (Hordeum vulgare) seed while a 30 kDa cysteine endoproteinase (EC 3.4.22) is one of the proteinases synthesized de novo in the germinating seed. In this work, the localization of these two acid proteinases was studied at both the tissue and subcellular levels by immunomicroscopy. The results confirm that they have completely different functions. The aspartic proteinase was present in the ungerminated seed and, during germination, it appeared in all the living tissues of the grain, including the shoot and root. Contrary to previous suggestions, it was not observed in the starchy endosperm. By immunoblotting…

Functional analysis of the cysteine residues and the repetitive sequence ofSaccharomyces cerevisiaePir4/Cis3: the repetitive sequence is needed for b…

2003

Identification of PIR/CIS3 gene was carried out by amino-terminal sequencing of a protein band released by β-mercaptoethanol (β-ME) from S. cerevisiae mnn9 cell walls. The protein was released also by digestion with β-1,3-glucanases (laminarinase or zymolyase) or by mild alkaline solutions. Deletion of the two carboxyterminal Cys residues (Cys214-12aa-Cys227-COOH), reduced but did not eliminate incorporation of Pir4 (protein with internal repeats) by disulphide bridges. Similarly, site-directed mutation of two other cysteine amino acids (Cys130Ser or Cys197Ser) failed to block incorporation of Pir4; the second mutation produced the appearance of Kex2-unprocessed Pir4. Therefore, it seems th…

Staphylococcal NreB: an O2-sensing histidine protein kinase with an O2-labile iron-sulphur cluster of the FNR type

2004

Summary The nreABC ( n itrogen re gulation) operon encodes a new staphylococcal two-component regulatory sys- tem that controls dissimilatory nitrate/nitrite reduc- tion in response to oxygen. Unlike other two- component sensors NreB is a cytosolic protein with four N-terminal cysteine residues. It was shown that both the NreB-cysteine cluster and Fe ions are required for function. Isolated NreB was converted to the active form by incubation with cysteine desul- phurase, ferrous ions and cysteine. This activation is typical for FeS-containing proteins and was reversed by oxygen. During reconstitution an absorption band at 420 nm and a yellow-brownish colour (typical for an FNR-type iron-sul…

Exploring new activating groups for reactive cysteine NCAs

2016

Abstract Due to its ability to reversibly crosslink proteins, cysteine has a unique role as an amino acid in nature. For controlled, asymmetric formation of disulfides from two thiols, one thiol needs to be activated. While few activating groups for cysteine have been proposed, they are usually not stable against amines making them unsuitable for solid phase peptide synthesis or amine initiated polymerization of α-amino acid-N-carboxy-anhydrides (NCAs). In this Letter we describe a series of new thiol activated cysteines, as well as their NCAs and explore the link between electron deficiency of the leaving group and control over NCA polymerization.

Poly(S-ethylsulfonyl-l-homocysteine): An α-Helical Polypeptide for Chemoselective Disulfide Formation

2018

Homocysteine and cysteine are the only natural occurring amino acids that are capable of disulfide bond formations in peptides and proteins. The chemoselective formation of asymmetric disulfide bonds, however, is chemically challenging and requires an activating group combining stability against hard nucleophiles, e.g., amines, with reactivity toward thiols and soft nucleophiles. In light of these considerations, we introduced the S-alkylsulfonyl cysteines in our previous work. Here, we present the synthesis and ring-opening polymerization of S-ethylsulfonyl-l-homocysteine N-carboxyanhydrides. We demonstrate that the polymerization leads to narrowly distributed polypeptides (Đ = 1.1–1.3) wi…

Poly(S-ethylsulfonyl-l-cysteines) for Chemoselective Disulfide Formation

2016

The amino acid cysteine possesses a unique role in nature due to its ability to reversibly cross-link proteins. To transfer this feature to polypeptides and control the process of disulfide formation, a protective group needs to provide stability against amines during synthesis, combined with chemoselective reactivity toward thiols. A protective group providing these unique balance of stability and reactivity toward different nucleophiles is the S-alkylsulfonyl group. In this work we report the polymerization of S-ethylsulfonyl-l-cysteine N-carboxyanhydride and kinetic evaluations with respect to temperature (−10, 0, and +10 °C) and monomer concentration. The polymerization degree of poly(S…

2020

The facile synthesis and detailed investigation of a class of highly potent protease inhibitors based on 1,4-naphthoquinones with a dipeptidic recognition motif (HN-l-Phe-l-Leu-OR) in the 2-position and an electron-withdrawing group (EWG) in the 3-position is presented. One of the compound representatives, namely the acid with EWG = CN and with R = H proved to be a highly potent rhodesain inhibitor with nanomolar affinity. The respective benzyl ester (R = Bn) was found to be hydrolyzed by the target enzyme itself yielding the free acid. Detailed kinetic and mass spectrometry studies revealed a reversible covalent binding mode. Theoretical calculations with different density functionals (DFT…