Oxidation of tyrosine residues in proteins by tyrosinase. Formation of protein-bonded 3,4-dihydroxyphenylalanine and 5-S-cysteinyl-3,4-dihydroxyphenylalanine.
Ontology highlight
ABSTRACT:
SUBMITTER: Ito S
PROVIDER: S-EPMC1144193 | biostudies-other | 1984 Sep
REPOSITORIES: biostudies-other
Similar Datasets
Project description:A series of phosphonic analogues of tyrosine and 3,4-dihydroxyphenylalanine (dopa) were synthesized in order to study their interaction with mushroom tyrosinase. 1-Amino-2-(3,4-dihydroxyphenyl)ethylphosphonic acid and 1-amino-2-(3,4-dimethoxyphenyl)ethylphosphonic acid turned out to be substrates for mushroom tyrosinase with Km values of 3.3 mM and 9.3 mM respectively. Shortening of the alkyl chain by one methylene group gave amino-(3,4-dihydroxyphenyl)methylphosphonic acid, one of the most powerful known inhibitors of this enzyme. This compound, racemic as well as in its optically active forms, exerts a mixed type of inhibition with an affinity for the enzyme one order of magnitude greater than that of the natural substrate.
| S-EPMC1147667 | biostudies-other
Project description:A major product of hydroxy-radical addition to tyrosine is 3, 4-dihydroxyphenylalanine (DOPA) which has reducing properties. Protein-bound DOPA (PB-DOPA) has been shown to be a major component of the stable reducing species formed during protein oxidation under several conditions. The aim of the present work was to investigate whether DOPA, and especially PB-DOPA, can mediate oxidative damage to DNA. We chose to generate PB-DOPA using mushroom tyrosinase, which catalyses the hydroxylation of tyrosine residues in protein. This permitted us to study the reactions of PB-DOPA in the virtual absence of other protein-bound oxidation products. The formation of two oxidation products of DNA, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8oxodG) and 5-hydroxy-2'-deoxycytidine (5OHdC), were studied with a novel HPLC using gradient elution and an electrochemical detection method, which allowed the detection of both DNA modifications in a single experiment. We found that exposure of calf thymus DNA to DOPA or PB-DOPA resulted in the formation of 8oxodG and 5OHdC, with the former predominating. The formation of these DNA oxidation products by either DOPA or PB-DOPA depended on the presence of oxygen, and also on the presence and on the concentration of transition metal ions, with copper being more effective than iron. The yields of 8oxodG and 5OHdC increased with DOPA concentration in proteins. Thus PB-DOPA was able to promote further radical-generating events, which then transferred damage to other biomolecules such as DNA.
| S-EPMC1219245 | biostudies-other
Project description:Tyrosinase usually catalyses the conversion of monophenols into o-diphenols and the oxidation of diphenols to the corresponding o-quinones. Sugumaran [(1986) Biochemistry 25, 4489-4492] has previously proposed an unusual oxidative decarboxylation of 3,4-dihydroxymandelate catalysed by tyrosinase. Our determination of the intermediates involved in the reaction demonstrated that 3,4-dihydroxybenzaldehyde is not the first intermediate appearing in the medium during the enzymic reaction. Re-examination of this new activity of tyrosinase has demonstrated that the product of the enzyme action is the o-quinone, which, owing to its instability, evolves to the final product, 3,4-dihydroxybenzaldehyde, by a chemical reaction of oxidative decarboxylation.
| S-EPMC1135465 | biostudies-other
Project description:Background3,4-Dihydroxyphenylalanine decarboxylase (DDC), also known as aromatic L-amino acid decarboxylase, catalyzes the decarboxylation of a number of aromatic L-amino acids. Physiologically, DDC is responsible for the production of dopamine and serotonin through the decarboxylation of 3,4-dihydroxyphenylalanine and 5-hydroxytryptophan, respectively. In insects, both dopamine and serotonin serve as classical neurotransmitters, neuromodulators, or neurohormones, and dopamine is also involved in insect cuticle formation, eggshell hardening, and immune responses.Principal findingsIn this study, we expressed a typical DDC enzyme from Drosophila melanogaster, critically analyzed its substrate specificity and biochemical properties, determined its crystal structure at 1.75 Angstrom resolution, and evaluated the roles residues T82 and H192 play in substrate binding and enzyme catalysis through site-directed mutagenesis of the enzyme. Our results establish that this DDC functions exclusively on the production of dopamine and serotonin, with no activity to tyrosine or tryptophan and catalyzes the formation of serotonin more efficiently than dopamine.ConclusionsThe crystal structure of Drosophila DDC and the site-directed mutagenesis study of the enzyme demonstrate that T82 is involved in substrate binding and that H192 is used not only for substrate interaction, but for cofactor binding of drDDC as well. Through comparative analysis, the results also provide insight into the structure-function relationship of other insect DDC-like proteins.
| S-EPMC2809104 | biostudies-literature
Project description:Fluorescence-based assays for hydrolases that cleave within the substrate (endopeptidases) are common, while developing substrates for proteases that selectively cleave from peptide termini (exopeptidases) is more challenging, since the termini are specifically recognized by the enzyme and cannot be modified to facilitate a Förster resonance energy transfer (FRET)-based approach. The development of a robust system that enables the quenching of fluorescent particles by simple amino acid side chains would find broad utility for peptide sensors and would be advantageous for exopeptidases. Here we describe a quantum dot (QD)-based electron transfer (ET) sensor that is able to allow direct, quantitative monitoring of both exopeptidase and endopeptidase activity. The incorporation of 3,4-dihydroxyphenylalanine (DOPA) into the sequence of a peptide allows for the quenching of QD photoluminescence through an ET mechanism. DOPA is a nonproteinogenic amino acid that can replace a phenylalanine or tyrosine residue in a peptide sequence without severely altering structural properties, allowing for its introduction at multiple positions within a biologically active peptide substrate. Consequently, the quenching system presented here is ideally suited for incorporation into diverse peptide substrates for enzyme recognition, digestion, and activity sensing. Our findings suggest a broad utility of a small ET-capable amino acid side chain in detecting enzyme activity through ET-mediated QD luminescence quenching.
| S-EPMC4968404 | biostudies-literature
Project description:The pancreatic β cells can synthesize dopamine by taking L-dihydroxyphenylalanine, but whether pancreatic acinar cells synthesize dopamine has not been confirmed. By means of immunofluorescence, the tyrosine hydroxylase -immunoreactivity and aromatic amino acid decarboxylase (AADC)- immunoreactivity were respectively observed in pancreatic acinar cells and islet β cells. Treatment with L-dihydroxyphenylalanine, not tyrosine, caused the production of dopamine in the incubation of INS-1 cells (rat islet β cell line) and primary isolated islets, which was blocked by AADC inhibitor NSD-1015. However, only L-dihydroxyphenylalanine, but not dopamine, was detected when AR42J cells (rat pancreatic acinar cell line) were treated with tyrosine, which was blocked by tyrosine hydroxylase inhibitor AMPT. Dopamine was detected in the coculture of INS-1 cells with AR42J cells after treatment with tyrosine. In an in vivo study, pancreatic juice contained high levels of L-dihydroxyphenylalanine and dopamine. Both L-dihydroxyphenylalanine and dopamine accompanied with pancreatic enzymes and insulin in the pancreatic juice were all significantly increased after intraperitoneal injection of bethanechol chloride and their increases were all blocked by atropine. Inhibiting TH with AMPT blocked bethanechol chloride-induced increases in L-dihydroxyphenylalanine and dopamine, while inhibiting AADC with NSD-1015 only blocked the dopamine increase. Bilateral subdiaphragmatic vagotomy of rats leads to significant decreases of L-dihydroxyphenylalanine and dopamine in pancreatic juice. These results suggested that pancreatic acinar cells could utilize tyrosine to synthesize L-dihydroxyphenylalanine, not dopamine. Islet β cells only used L-dihydroxyphenylalanine, not tyrosine, to synthesize dopamine. Both L-dihydroxyphenylalanine and dopamine were respectively released into the pancreatic duct, which was regulated by the vagal cholinergic pathway. The present study provides important evidences for the source of L-dihydroxyphenylalanine and dopamine in the pancreas.
| S-EPMC8649935 | biostudies-literature
Project description:Amino acid radical generation and transport are fundamentally important to numerous essential biological processes to which small molecule models lend valuable mechanistic insights. Pyridyl-amino acid-methyl esters are appended to a rhenium(I) tricarbonyl 1,10-phenanthroline core to yield rhenium-amino acid complexes with tyrosine ([Re]-Y-OH) and phenylalanine ([Re]-F). The emission from the [Re] center is more significantly quenched for [Re]-Y-OH upon addition of base. Time-resolved studies establish that excited-state quenching occurs by a combination of static and dynamic mechanisms. The degree of quenching depends on the strength of the base, consistent with a proton-coupled electron transfer (PCET) quenching mechanism. Comparative studies of [Re]-Y-OH and [Re]-F enable a detailed mechanistic analysis of a bidirectional PCET process.
| S-EPMC3594118 | biostudies-literature
Project description:1. Melanosomal tyrosinase was isolated from normal C57B1 mice, and a comparison of the tyrosine-hydroxylation and dopa (3,4-dihydroxyphenylalanine)-oxidation activities of this enzyme was made. 2. The results indicate that in the absence of dopa cofactor, this enzyme is capable of tyrosine hydroxylation, but with very little subsequent dopa oxidation and melanin formation. 3. This mechanism of enzyme action may play an important role in the intracellular regulation of melanin formation. 4. Further, dopa appears to act as a positive allosteric effector for tyrosine hydroxylation by tyrosinase, in addition to its known activity as a hydrogen donor for the reaction.
| S-EPMC1163896 | biostudies-other
Project description:The study of DOPA (3,4-dihydroxyphenylalanine) decarboxylase by steady-state methods is difficult because multiple reactions occur. The reaction with DOPA was studied at enzyme concentrations between 20 and 50 micrometer by direct observation of the bound coenzyme by using stopped-flow and conventional spectrophotometry. Four processes were observed on different time scales and three of these were attributed to stages in the decarboxylation. The fourth was attributed to an accompanying transamination that renders the enzyme inactive. It was clear that much, if not all, of the 330 nm-absorbing coenzyme present in the free enzyme plays an active part in the decarboxylation, since it is converted into 420 nm-absorbing material in the first observable step. An intermediate absorbing maximally at 390 nm is formed in a slower step. Rate and equilibrium constants have been determined and the ratio of decarboxylation to transamination was estimated to be 1200:1.
| S-EPMC1161566 | biostudies-other
Project description:The conversion of tyrosine into dopa [3-(3,4-dihydroxyphenyl)alanine] is the rate limiting step in the biosynthesis of melanins catalysed by tyrosinase. This hydroxylation reaction is characterized by a lag period, the extent of which depends on various parameters, notably the presence of a suitable hydrogen donor such as dopa or tetrahydropterin. We have now found that catalytic amounts of Fe2+ ions have the same effect as dopa in stimulating the tyrosine hydroxylase activity of the enzyme. Kinetic experiments showed that the shortening of the induction time depends on the concentration of the added metal and the nature of the buffer system used and is not suppressed by superoxide dismutase, catalase, formate or mannitol. Notably, Fe3+ ions showed only a small delaying effect on tyrosinase activity. Among the other metals which were tested, Zn2+, Co2+, Cd2+ and Ni2+ had no detectable influence, whereas Cu2+ and Mn2+ exhibited a marked inhibitory effect on the kinetics of tyrosine oxidation. These findings are discussed in the light of the commonly accepted mechanism of action of tyrosinase.
| S-EPMC1145033 | biostudies-other