Action of Tyrosinase on Ortho-Substituted Phenols: Possible Influence on Browning and Melanogenesis

Abstract

The action of tyrosinase on ortho-substituted monophenols (thymol, carvacrol, guaiacol, butylated hydroxyanisole, eugenol, and isoeugenol) was studied. These monophenols inhibit melanogenesis because they act as alternative substrates to L-tyrosine and L-Dopa in the monophenolase and diphenolase activities, respectively, despite the steric hindrance on the part of the substituent in ortho position with respect to the hydroxyl group. We kinetically characterize the action of tyrosinase on these substrates and assess its possible effect on browning and melanognesis. In general, these compounds are poor substrates of the enzyme, with high Michaelis constant values, K(m), and low catalytic constant values, k(cat), so that the catalytic efficiency k(cat)/K(m) is low: thymol, 161 ± 4 M(-1) s(-1); carvacrol, 95 ± 7 M(-1) s(-1); guaiacol, 1160 ± 101 M(-1) s(-1).

Skin Whitening Cosmetics: Feedback and Challenges in the Development of Natural Skin Lighteners

“…This might be due to the compounds present in these types of extracts (mainly mono-and sesquiterpenes). This observation already shows through the literature survey: compared to solvent extracts, only a few studies report the tyrosinase inhibition and/or anti-melanogenic effects of such extracts or of individual EOs' constituents [87,166,[176][177][178][179][180][181]. Single components, mainly acting as alternative substrates to L-Tyrosine and L-DOPA (eugenol, thymol, etc.…”

“…Single components, mainly acting as alternative substrates to L-Tyrosine and L-DOPA (eugenol, thymol, etc. ), have been proven to be quite effective [177]. Nevertheless, the overall composition of the EO influences its bioactivity via synergism/antagonism and might be the reason for such poor screening results.…”

Katalytische Phenolhydroxylierung mit Sauerstoff: Substratvielfalt jenseits der Proteinmatrix von Tyrosinase

“…So kann diese ortho-Hydroxylierungschemie auf Substrate jenseits des enzymatischen Substratspektrums übertragen werden. [26] Die [22,27] ähnlich demjenigen für Oxy-Tyrosinase und Oxy-Hämocyanin. [29] Die Bande nahe 412 nm (0.9 mm À1 cm À1 ) wird anhand einer Natural-Transition-Orbital-Analyse eines TD-DFT-berechneten Spektrums (Abbildung 1 B; TD-DFT = zeitabhängige Dichtefunktionaltheorie) einem Pyrazol/Pyridin-p*!d xy -ChargeTransfer-Übergang zugeordnet.…”

“…[32] Wahrscheinlich wird dies durch den großen sterischen Anspruch der anellierten Ringstruktur in ortho-Position zum Phenolsauerstoffatom verursacht (Tabelle 1 B). [26] 1 oxidiert 8-Hydroxychinolin sowohl stçchiometrisch bei À78 8C zum Catechol (7,8-Dihydroxychinolin) als auch katalytisch zum Chinon bei 25 8C (Chinolin-7,8-dion; acht Zyklen; Tabelle 1 B), was das Substratspektrum deutlich gegenüber dem des enzymatischen Systems erweitert. [2] Die Substratflexibilität von 1 macht es zu einem potenziell nützlichen Reagens für effiziente stçchiometrische Umsetzungen einer großen Vielfalt von Phenolaten zu Catecholen oder auch zu einem effektiven Katalysator für die Oxidation von Phenolen zu Chinonen mit Disauerstoff; diese Chinone kçnnen anschließend leicht zu Catecholen reduziert werden.…”

Hydrogen Peroxide Helps in the Identification of Monophenols as Possible Substrates of Tyrosinase

“…24) Recently, it was found that they act as tyrosinase substrates when the catalytic quantities of the corresponding O-diphenol are added. 25) The reaction observed in the presence of H 2 O 2 clearly indicated that they are substrates of the enzyme. (b) indicates how an increase in substrate concentration compared with (a) increased the velocity of the reaction.…”