Epigallocatechin and epigallocatechin-3-gallate are not inhibitors of tyrosinase.

Inhibition of tyrosinase by gallic acid, epigallocatechin, and epigallocatechin-3-gallate has been recently described in several publications. However, oxidation of these compounds by this enzyme was demonstrated long time ago. Gallic acid also reduced tyrosinase-generated o-quinones.

Oxidation of anti-thyroid drugs and their selenium analogs by ABTS radical cation.

Lactoperoxidase was previously used as a model enzyme to test the inhibitory activity of selenium analogs of anti-thyroid drugs with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a substrate. Peroxidases oxidize ABTS to a metastable radical ABTS, which is readily reduced by many antioxidants, including thiol-containing compounds, and it has been used for decades to measure antioxidant activity in biological samples. We showed that anti-thyroid drugs 6-n-propyl-2-thiouracil, methimazole, and selenium analogs of methimazole also reduced it rapidly.

Oxidation of baicalein by tyrosinase and by o-quinones.

Baicalein (5,6,7-trihydroxyflavone) has been previously described as an inhibitor of tyrosinase (Guo et al. Int. J.

Rifampicin is not an inhibitor of tyrosinase.

Rifampicin has been previously described as an inhibitor of tyrosinase (Chai et al., Int. J.

Comment on "Natural and synthetic flavonoid derivatives as new potential tyrosinase inhibitors: a systematic review" by R. Obaid, E. Mughal, N. Naeem, A. Sadiq, R. Alsantali, R. Jassas, Z. Moussa and S. Ahmed, , 2021, , 22159.

A review article has been published recently (, 2021, , 22159-22198) describing flavonoids as inhibitors of tyrosinase. However, many compounds included in this review have been previously shown to act as substrates of this enzymes or antioxidants reducing tyrosinase-generated -quinones. Products of their oxidation absorb light in a range different than dopachrome, the oxidation product of l-tyrosine or l-dopa, whose concentration is measured spectrophotometrically in the standard enzymatic assay to monitor the activity of this enzyme.

Quercetin is a substrate not an inhibitor of tyrosinase - comments on "Quercetin as a tyrosinase inhibitor: Inhibitory activity, conformational change and mechanism" published by Fan et al. (2017).

Quercetin was described as an inhibitor of tyrosinase in an article published in Food Research International. However, it was firmly established in the literature before that this compound was a substrate of this enzyme and an antioxidant reducing tyrosinase-generated o-quinones.

In vitro oxidation of hispidin and gallic acid by horseradish peroxidase.

Gallic acid and hispidin have been previously described by us as inhibitors of horseradish peroxidase (Benarous, K., Benali, F. Z.

Synthesis of disparlure and monachalure enantiomers from 2,3-butanediacetals.

2,3-Butanediacetal derivatives were used for the stereoselective synthesis of unsymmetrically substituted -epoxides. The procedure was applied for the preparation of both enantiomers of disparlure and monachalure, the components of the sex pheromones of the gypsy moth () and the nun moth () using methyl (2,3,5,6)-3-ethylsulfanylcarbonyl-5,6-dimethoxy-5,6-dimethyl-1,4-dioxane-2-carboxylate as the starting material.

Mechanisms of interference of p-diphenols with the Trinder reaction.

p-Diphenols, such as homogentisic acid, gentisic acid, etamsylate, and calcium dobesilate, interfere with diagnostic tests utilizing the Trinder reaction but the mechanisms of these effects are not fully understood. We observed substantial differences both in oxidation of p-diphenols by horseradish peroxidase and their influence on oxidation of 4-aminoantipyrine and various phenolic substrates. Homogentisic acid was rapidly oxidized by the enzyme and completely blocked chromophore formation.

Collisional mechanism of ligand release by Bombyxmori JHBP, a member of the TULIP / Takeout family of lipid transporters.

Juvenile hormones (JHs) regulate important processes in insects, such as postembryonic development and reproduction. In the hemolymph of Lepidoptera, these lipophilic sesquiterpenic hormones are transported from their site of synthesis to target tissues by high affinity carriers, the juvenile hormone binding proteins (JHBPs). Lepidopteran JHBPs belong to a recently uncovered, yet very ancient family of proteins sharing a common lipid fold (TULIP domain) and involved in shuttling various lipid ligands.

Interference of carbidopa and other catechols with reactions catalyzed by peroxidases.

Background: A number of compounds, including ascorbic acid, catecholamines, flavonoids, p-diphenols and hydrazine derivatives have been reported to interfere with peroxidase-based medical diagnostic tests (Trinder reaction) but the mechanisms of these effects have not been fully elucidated.

Methods: Reactions of bovine myeloperoxidase with o-dianisidine, bovine lactoperoxidase with ABTS and horseradish peroxidase with 4-aminoantipyrine/phenol in the presence of carbidopa, an anti-Parkinsonian drug, and other catechols, including l-dopa, were monitored spectrophotometrically and by measuring hydrogen peroxide consumption.

Results: Chromophore formation in all three enzyme/substrate systems was blocked in the presence of carbidopa and other catechols.

Reactions of Flavonoids with o-Quinones Interfere with the Spectrophotometric Assay of Tyrosinase Activity.

Flavonoids are important food components with antioxidant properties and many of them have been described as tyrosinase inhibitors. Oxidation of quercetin, kaempferol, morin, catechin, and naringenin by mushroom tyrosinase and their influence on the oxidation of l-dopa and l-tyrosine was studied. Reaction rates measured spectrophotometrically and by oxygen consumption differed substantially.

Synthesis of the aggregation pheromone of the Colorado potato beetle from its degradation product.

Incubation of the Colorado potato beetle aggregation pheromone, (S)-1,3-dihydroxy-3,7-dimethyl-6-octen-2-one, with antennal or leg extracts from this beetle gave 6-methyl-5-hepten-2-one as the major product. This ketone was used as a substrate in a stereoselective synthesis of the pheromone. It was attached to the butanediacetal of glycolic acid with good stereoselectivity and the desired isomer was further enriched by purification of the product of this reaction on silica gel.

Synthesis and analysis of activity of a potential anti-melanoma prodrug with a hydrazine linker.

A potential anti-melanoma prodrug containing a phenolic activator, a hydrazine linker, and a nitrogen mustard effector - (N-{4-[bis-(2-chloroethyl)amino]benzoyl}-N'-(4-hydroxybenzyl)hydrazine) has been synthesized in seven steps. Spectrophotometric measurements of its oxidation by tyrosinase showed a rapid increase of absorbance at 337 nm. HPLC analysis demonstrated that two major products were formed.

Oxidation of carbidopa by tyrosinase and its effect on murine melanoma.

Oxidation of the anti-Parkinsonian agent carbidopa by tyrosinase was investigated. The products of this reaction were identified as 3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid and 6,7-dihydroxy-3-methylcinnoline. These results demonstrate that after oxidation of the catechol moiety to an o-quinone either a redox exchange with the hydrazine group or a cyclization reaction occur.

Indirect oxidation of the antitumor agent procarbazine by tyrosinase--possible application in designing anti-melanoma prodrugs.

The interaction of tyrosinase with the anticancer drug procarbazine has been investigated. In the presence of the enzyme alone no oxidation of this dialkylhydrazine above the background level was observed. However, when phenolic substrates (4-tert-butylcatechol or N-acetyl-l-tyrosine) were included in the reaction mixture, procarbazine was rapidly degraded.

Indirect oxidation of amino acid phenylhydrazides by mushroom tyrosinase.

We have investigated oxidation of amino acid phenylhydrazides by mushroom tyrosinase in the presence of 4-tert-butylcatechol and N-acetyl-L-tyrosine. Spectrophotometric measurements showed gradual disappearance of 4-tert-butyl-o-benzoquinone, generated by oxidation of 4-tert-butylcatechol with sodium periodate, after addition of amino acid phenylhydrazides. However, the presence of the phenylhydrazides did not influence the concentration of 4-tert-butyl-o-benzoquinone formed during enzymatic oxidation.

Interaction of mushroom tyrosinase with aromatic amines, o-diamines and o-aminophenols.

3-Amino-L-tyrosine was found to be a substrate of mushroom tyrosinase, contrary to what had previously been reported in the literature. A series of amino derivatives of benzoic acid were tested as substrates and inhibitors of the enzyme. 3-Amino-4-hydroxybenzoic acid, 4-amino-3-hydroxybenzoic acid and 3,4-diaminobenzoic acid were oxidized by this enzyme, as previously reported for Neurospora crassa tyrosinase, but 4-aminobenzoic acid and 3-aminobenzoic acid were not.

Analysis of involvement of the 3'-untranslated regions in regulating mRNA stability for vitellogenin, cyanoprotein alpha, and cyanoprotein beta from the bean bug, Riptortus clavatus.

The degradation of the 3'-untranslated regions (UTRs) of vitellogenin, cyanoprotein alpha, and cyanoprotein beta from the bean bug, Riptortus clavatus, was analyzed in vitro. The degradation pattern was similar for all three RNAs, with a high degradation rate in non-diapausing adult insects and no degradation in the fifth instar nymphs and in diapausing adults, and was not correlated with the expression levels of these three proteins. Proteins binding to the 3'-UTRs were detected in polysomal and cytosolic extracts.

Redox reaction between amino-(3,4-dihydroxyphenyl)methyl phosphonic acid and dopaquinone is responsible for the apparent inhibitory effect on tyrosinase.

Amino-(3,4-dihydroxyphenyl)methyl phosphonic acid, the phosphonic analog of 3,4-dihydroxyphenylglycine, had been previously reported as a potent inhibitor of tyrosinase. The mechanism of the apparent enzyme inhibition by this compound has now been established. Amino-(3,4-dihydroxyphenyl)methyl phosphonic acid turned out to be a substrate and was oxidized to o-quinone, which evolved to a final product identified as 3,4-dihydroxybenzaldehyde, the same as for 3,4-dihydroxyphenylglycine.

Degradation of an alkaloid pheromone from the pale-brown chafer, Phyllopertha diversa (Coleoptera: Scarabaeidae), by an insect olfactory cytochrome P450.

The pale-brown chafer, Phyllopertha diversa, utilizes an unusual alkaloid, 1,3-dimethyl-2,4-(1H,3H)-quinazolinedione, as its sex pheromone. This compound is rapidly degraded in vitro by the antennal protein extracts from this scarab beetle. Demethylation at the N-1 position and hydroxylation of the aromatic ring have been identified as the major catabolic pathways.

Conformational change in the pheromone-binding protein from Bombyx mori induced by pH and by interaction with membranes.

The pheromone-binding protein (PBP) from Bombyx mori was expressed in Escherichia coli periplasm. It specifically bound radiolabeled bombykol, the natural pheromone for this species. It appeared as a single band both in native and SDS-polyacrylamide gel electrophoresis and was also homogeneous in most chromatographic systems.

Identification and cloning of odorant binding proteins from the scarab beetle Phyllopertha diversa.

Wehave identified, cloned, and characterized two odorant binding proteins from the pale brown chafer, Phyllopertha diversa. One of the proteins (OBP1, 116 amino acids long) showed high amino acid identity (>90%) to two previously identified PBPs from scarab beetles. The second protein (OBP2) showed limited sequence similarity to lepidopteran and dipteran OBPs, but contained only 133 amino acids.