Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Leu-enkephalin and Met-enkephalin are oxidized in vitro by mushroom and sepia tyrosinase giving rise to synthetic melanins whose production is dependent on incubation time and on enzyme concentration. The Enk-melanins formed are acid-insoluble brownish or reddish pigments showing a continuous absorbance in the visible region when dissolved in basic solution. The presence of the amino acid chain makes them fully soluble in pH 7.4 0.05 M phosphate buffer and methanol.
 ...
PMID:Melanins production from enkephalins by tyrosinase. 159 Jul 83

A new tyrosine-specific LC assay with pre-column fluorogenic derivatization is described for Tyr-Gly as model peptide. o-Hydroxylation of the tyrosine residue with tyrosinase in the presence of ascorbic acid, followed by oxidation to the corresponding quinone by potassium ferricyanide at room temperature and condensation with 1,2-diamino-1,2-diphenylethane in the presence of acetonitrile gave a highly fluorescent species. The resulting fluorescence signal was stable over the investigated period of 5 h and exhibited a linear response curve on a reversed-phase LC system. Under optimized reaction conditions, the lower limit of detection for Tyr-Gly was 200 fmol per injection. Examination of a series of dipeptides (L-Tyr-L-X; X = Gly, Ala, Val, Leu, Phe) showed no significant influence of neighbouring amino acids on the enzymatic hydroxylation by tyrosinase. This and the formation of a highly fluorescent signal for Leu-enkephalin suggests the general feasibility of the approach for the determination of tyrosine-containing peptides.
 ...
PMID:A new fluorogenic assay for tyrosine-containing peptides. 181 76

Tyrosinase activity was tested on some tyrosine-containing peptides (enkephalins and exorphins). All they are substrates for tyrosinase, showing a good affinity for the enzyme, in some cases higher than tyrosine itself. Aminoacid analysis after hydrolysis of long-lasting incubation mixtures of tyrosinase with Leu-enkephalin in presence of reductants demonstrates the formation of DOPA. The production of a new peptide containing DOPA derived from the oxidation of Leu-enkephalin was revealed by high performance liquid chromatography (HPLC).
 ...
PMID:Enkephalins and exorphins oxidation by tyrosinase. 251 78

In vitro experiments are reported showing that NAD(P)H:(quinone acceptor) oxidoreductase (QR), purified from Glycine max seedlings, reduces Leu- and Met-enkephalin-tyrosinase oxidation products, in the presence of NADH or NADPH. QR was not capable to catalyze the reduction of N-acetyl-dopaquinone formed by the cation of mushroom tyrosinase on N-acetyl-L-tyrosine, while it was able to reduce dopachrome. The results support the hypothesis that QR can inhibit the formation of melanin-like compounds, as catalyzed by the action of tyrosinase on Leu-enkephalin and Met-enkephalin. It is proposed that, in the presence of NAD(P)H as the electron donor, the inhibition occurs by the specific conversion of the dopachrome-derivative into the reduced precursor, leucodopachrome-derivative.
 ...
PMID:Effect of NAD(P)H:quinone oxidoreductase on tyrosinase-mediated oxidation of opioid neuropeptides Leu-enkephalin and Met-enkephalin. 867 15

The oxidation of opioid peptides by tyrosinase in the presence of an excess of a thiol gives rise to cysteinyldopa derivatives. The major products arising from the reaction between Leu-enkephalin and cysteine are represented by 5-S-cysteinyldopaenkephalin (5-CDenk) and 2-S-cysteinyldopaenkephalin (2-CDenk). The interaction of 5-CDenk and 2-CDenk with reactive oxygen species (ROS) has been studied. These compounds are able to scavenge superoxide anion, hydroxyl and peroxyl radicals as well as to reduce the lipid peroxidation rate induced by ABAP. The scavenging activities in all instances are dose-dependent. In some cases CDenks are more active than compounds recognized as strong radical scavengers, such as Trolox and mannitol. As a result of the action of the Fenton system, the CDenks (as well as the Enks) are oxidized into pigmented derivatives. The possible implications of the interaction of CDenks and Enks with ROS on melanization process in Parkinson's disease are discussed.
 ...
PMID:Interaction of enkephalin derivatives with reactive oxygen species. 1134 52

Tetrahydroisoquinolines (TIQs) are endogenous alkaloid compounds deriving from the non-enzymatic Pictet-Spengler condensation of catecholamines with aldehydes. These compounds are able to unsettle catecholamines uptake and release from synaptosomes and have been detected in urine and in post-mortem Parkinsonian brains. We have obtained in vitro, by the reaction of dopa-enkephalin (dopa-Gly-Gly-Phe-Leu) with acetaldehyde in the presence of rameic ions, a TIQ derivative of Leu-enkephalin. The isolation and the recovery of the peptide was obtained by HPLC. The acid hydrolysis and the subsequent analysis of the peptide lysate by the Amino acid analyser clearly revealed the absence of dopa, while the electrospray ionisation mass spectrometry showed that the sequence of the enkephalin derivative was the following: 3-carboxy-salsolinol-Gly-Gly-Phe-Leu (TIQ-enkephalin). This compound was not a good substrate for microsomal aminopeptidase and pronase with respect to Leu-enkephalin. Tested in the binding assay, the TIQ-enkephalin exhibited a very poor affinity toward the enkephalin receptors. When the TIQ-enkephalin was incubated with tyrosinase or peroxidase/H(2)O(2), the formation of TIQ-opio-melanins occurred.
 ...
PMID:Tetrahydroisoquinoline derivatives of enkephalins: synthesis and properties. 1203 73