The Relationship between the IC Values and the Apparent Inhibition Constant in the Study of Inhibitors of Tyrosinase Diphenolase Activity Helps Confirm the Mechanism of Inhibition.

Tyrosinase is the enzyme involved in melanization and is also responsible for the browning of fruits and vegetables. Control of its activity can be carried out using inhibitors, which is interesting in terms of quantitatively understanding the action of these regulators. In the study of the inhibition of the diphenolase activity of tyrosinase, it is intriguing to know the strength and type of inhibition.

Enzymatic oxidation of oleuropein and 3-hydroxytyrosol by laccase, peroxidase, and tyrosinase.

The oxidation of oleuropein and 3-hydroxytyrosol by oxidases laccase, tyrosinase, and peroxidase has been studied. The use of a spectrophotometric method and another spectrophotometric chronometric method has made it possible to determine the kinetic parameters V and K for each enzyme. The highest binding affinity was shown by laccase.

Kinetic characterization of the oxidation of catecolamines and related compounds by laccase.

The pathways of melanization and sclerotization of the cuticle in insects are carried out by the action of laccases on dopamine and related compounds. In this work, the laccase action of Trametes versicolor (TvL) on catecholamines and related compounds has been kinetically characterized. Among them, dopamine, l-dopa, l-epinephrine, l-norepinephrine, dl-isoprenaline, l-isoprenaline, dl-α-methyldopa, l-α-methyldopa and l-dopa methylester.

Structural and kinetic considerations on the catalysis of deoxyarbutin by tyrosinase.

Deoxyarbutin, a potent inhibitor of tyrosinase, could act as substrate of the enzyme. Oxytyrosinase is able to hydroxylate deoxyarbutin and finishes the catalytic cycle by oxidizing the formed o-diphenol to quinone, while the enzyme becomes deoxytyrosinase, which evolves to oxytyrosinase in the presence of oxygen. This compound is the only one described that does not release o-diphenol after the hydroxylation step.

Action of tyrosinase on alpha and beta-arbutin: A kinetic study.

The known derivatives from hydroquinone, α and β-arbutin, are used as depigmenting agents. In this work, we demonstrate that the oxy form of tyrosinase (oxytyrosinase) hydroxylates α and β-arbutin in ortho position of the phenolic hydroxyl group, giving rise to a complex formed by met-tyrosinase with the hydroxylated α or β-arbutin. This complex could evolve in two ways: by oxidizing the originated o-diphenol to o-quinone and deoxy-tyrosinase, or by delivering the o-diphenol and met-tyrosinase to the medium, which would produce the self-activation of the system.

Spectrophotometric Characterization of the Action of Tyrosinase on p-Coumaric and Caffeic Acids: Characteristics of o-Caffeoquinone.

New methods are proposed to determine the activity of tyrosinase on caffeic and p-coumaric acids. Because o-quinone from caffeic acid is unstable in its presence, it has been characterized through spectrophotometric measurements of the disappearance of coupled reducing agents, such as nicotinamide adenine dinucleotide reduced form. It has also been characterized by a chronometric method, measuring the time that a known concentration of ascorbic acid takes to be consumed.

Action of 2,2',4,4'-tetrahydroxybenzophenone in the biosynthesis pathway of melanin.

2,2',4,4'-tetrahydroxybenzophenone (Uvinul D50), a sunscreen used in cosmetics, has two effects in the melanin biosynthesis pathway. On the one hand, it acts a weak inhibitor of tyrosinase and on the other, it accelerates the conversion of dopachrome to melanin. Uvinul D50 was seen to behave as a weak competitive inhibitor: apparent constant inhibition=2.

Characterization of the action of tyrosinase on resorcinols.

The action of tyrosinase on resorcinol and some derivatives (4-ethylresorcinol, 2-methylresorcinol and 4-methylresorcinol) was investigated. If the catalytic cycle is completed with a reductant such as ascorbic acid or an o-diphenol such as 4-tert-butylcatechol, these compounds act as substrates of tyrosinase in all cases. The reaction can also be carried out, adding hydrogen peroxide to the medium.

4-n-butylresorcinol, a depigmenting agent used in cosmetics, reacts with tyrosinase.

4-n-Butylresorcinol (BR) is considered the most potent inhibitor of tyrosinase, which is why it is used in cosmetics as a depigmenting agent. However, this work demonstrates that BR is a substrate of this enzyme. The Em (met-tyrosinase) form is not active on BR, but Eox (oxy-tyrosinase) can act on this molecule, hydroxylating it to o-diphenol.