1,721,052 research outputs found
Enzymatic, stereoselective synthesis of (S)-norcoclaurine.
No full textAn efficient, stereoselective, synthesis of (S)-norcoclaurine has been developed using the recombinant (S)-norcoclaurine synthase (NCS) enzyme, starting from tyrosine and dopamine substrates in a one-pot, two steps process1-3. The first step of the biotransformation consists in the oxidative decarboxylation of tyrosine (1) by stoichiometric amounts of sodium hypochlorite in order to generate 4-hydroxyphenylacetadehyde (2). In the second step NCS and dopamine (3) substrate are added in the reaction mix in the presence of ascorbate (necessary to prevent oxidation of the catechol moiety). Quantitative extraction of the newly formed (S)-norcoclaurine (4) from the aqueous solution was achieved by adsorption on active charcoal, dispersed in the reaction mixture. The optimized process afforded enantiomerically pure (S)-norcoclaurine (93 %) with a yield higher than 80% and allowed good recovery of the enzyme for recycling
Determination of aminoethylcysteine ketimine decarboxylated dimer in human plasma and cultured cells by high-performance liquid chromatography with electrochemical detection
No full textAminoethylcysteine ketimine decarboxylated dimer (AECK-DD) is a natural compound with antioxidant properties of a new family of sulfur-containing amino acids. It has been detected in human urine and plasma, in mammalian cerebellum and, more recently, in dietary vegetables. In the present study, a simple, highly sensitive method using a high-performance liquid chromatography system with electrochemical detection (ECD) has been developed. The method showed excellent precision and accuracy. It has been found to be about 100-fold more sensitive than gas chromatographic method and 2000-fold more sensitive in respect to the liquid chromatography method with UV detection. The method showed the required features of specificity and sensitivity to detect aminoethylcysteine ketimine decarboxylated dimer in human plasma and in cultured cells after in vitro supplementation. (C) 2003 Elsevier B.V. All rights reserved
Aminoethylcysteine ketimine decarboxylated dimer detected in normal human urine by gas-liquid chomatography, selected-ion monitoring and mass spectrometry
No full textAminoethylcysteine ketimine is a biochemical product known to be converted spontaneously in the decarboxylated dimer. Since the ketimine has been detected in a mammalian brain, it was assumed that also the dimer could be present in the mammalian body and eventually excreted in the urine. Using human urine as the biological source, an extract was prepared which, submitted to gas-liquid chromatography, selected-ion monitoring and mass spectrometry, indicated the presence of the dimer
Antioxidant properties of the decarboxylated dimer of aminoethylcysteine ketimine: assessment of its ability to scavenge peroxynitrite.
No full textThe natural sulfur compound aminoethylcysteine ketimine decarboxylated dimer (AECK dimer) has been investigated for its ability to act as peroxynitrite scavenger. It has been found that the product efficiently protects against the nitration of tyrosine and the inactivation of oz-antiproteinase by peroxynitrite. The tyrosine nitration can be completely prevented by 100 mu M AECK dimer which appears as effective as the antioxidants glutathione and N-acetylcysteine. The AECK dimer was also found to limit surface charge alteration of low density lipoprotein induced by peroxynitrite. These findings indicate that the AECK dimer is a strong protective agent against peroxynitrite damage and that it could play an important role in the defence against oxidative stress in human diseases
Norcoclaurine Synthase: Mechanism of an Enantioselective Pictet-Spengler Catalyzing Enzyme
No full textThe use of bifunctional catalysts in organic synthesis finds inspiration in the selectivity of enzymatic catalysis which arises from the specific interactions between basic and acidic amino acid residues and the substrate itself in order to stabilize developing charges in the transition state. Many enzymes act as bifunctional catalysts using amino acid residues at the active site as Lewis acids and Lewis bases to modify the substrate as required for the given transformation. They bear a clear advantage over non-biological methods for their ability to tackle problems related to the synthesis of enantiopure compounds as chiral building blocks for drugs and agrochemicals. Moreover, enzymatic synthesis may offer the advantage of a clean and green synthetic process in the absence of organic solvents and metal catalysts. In this work the reaction mechanism of norcoclaurine synthase is described. This enzyme catalyzes the Pictet-Spengler condensation of dopamine with 4-hydroxyphenylacetaldehyde (4-HPAA) to yield the benzylisoquinoline alkaloids central precursor, (S)-norcoclaurine. Kinetic and crystallographic data suggest that the reaction mechanism occurs according to a typical bifunctional catalytic process
The oxidation of the sulfinates, hypotaurine and cysteine sulfinate, by carbonate radical anion.
No full textA domain swap approach reveals the plant wall-associated kinase 1 as a receptor of oligogalacturonides
No full text(R)-1-Arylethanols from aryl iodides through a two-step one-pot enantioselective chemoenzymatic process
No full text(R)-1-Arylethanols have been prepared in high to excellent overall yields through a two-step one-pot process that involves the palladium-catalyzed conversion of aryl iodides into the corresponding acetophenones, in the presence of acetic anhydride. EtN(i-Pr)(2), LiCl, and Pd(2)(dba)(3) followed by an enantioselective reduction step catalyzed by the alcohol dehydrogenase enzyme from Lactobacillus brevis. (C) 2009 Elsevier B.V. All rights reserved
Ethylene production in Botrytis cinerea- and oligogalacturonide - induced immunity requires calcium-dependent protein kinases
No full textPlant immunity against pathogens is achieved through rapid activation of defense responses that occur upon sensing of microbe- or damage-associated molecular pattern, respectively referred to as MAMPs and DAMPs. Oligogalacturonides (OGs), linear fragments derived from homogalacturonan hydrolysis by pathogen-secreted cell wall-degrading enzymes, and flg22, a 22-amino acid peptide derived from the bacterial flagellin, represent prototypical DAMPs and MAMPs, respectively. Both types of molecules induce protection against infections. In plants, like in animals, calcium is a second messenger that mediates responses to biotic stresses by activating calcium-binding proteins. Here we show that simultaneous loss of calcium-dependent protein kinases (CDPKs) CPK5, CPK6 and CPK11 affects Arabidopsis thaliana basal as well as elicitor- induced resistance to the necrotroph Botrytis cinerea, by affecting pathogen-induced ethylene production and accumulation of the ethylene biosynthetic enzymes 1-aminocyclopropane-1-carboxylic acid (ACC) synthase 2 (ACS2) and 6 (ACS6). Moreover, ethylene signaling contributes to OG-triggered immunity activation, and lack of CPK5, CPK6 and CPK11 affects the duration of OG- and flg22-induced gene expression, indicating that these kinases are shared elements of both DAMP and MAMP signaling pathways. This article is protected by copyright. All rights reserved
A domain swap approach reveals a role of the plant wall-associated kinase 1 (WAK1) as a receptor of oligogalacturonides
No full textOligogalacturonides (OGs) released from the plant cell wall are active both as damage-associated molecular patterns (DAMPs) for the activation of the plant immune response and regulators of plant growth and development. Members of the Wall-Associated Kinase (WAK) family are candidate receptors of OGs, due to their ability to bind in vitro these oligosaccharides. Because lethality and redundancy have hampered the study of WAKs by reverse genetics, we have adopted a chimeric receptor approach to elucidate the role of Arabidopsis WAK1. In a test-of-concept study, we first defined the appropriate chimera design and demonstrated that the Arabidopsis pattern recognition receptor (PRR) EFR is amenable to the construction of functional and resistance-conferring chimeric receptors carrying the ectodomain of another Arabidopsis PRR, FLS2. After, we analyzed chimeras derived from EFR and WAK1. Our results show that, upon stimulation with OGs, the WAK1 ectodomain is capable of activating the EFR kinase domain. On the other hand, upon stimulation with the cognate ligand elf18, the EFR ectodomain activates the WAK1 kinase, triggering defense responses that mirror those normally activated by OGs and are effective against fungal and bacterial pathogens. Finally, we show that transgenic plants overexpressing WAK1 are more resistant to Botrytis cinerea
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