Action of tyrosinase on TBC in the presence of D-Arb.

<p>The increase of absorbance was followed at 410 nm by means of a total oxygen consumption test, carried out in the presence of TBC and different concentrations of D-Arb (mM): a) 0, b) 0.1, c) 0.2 and d) 0.4. The rest of the experimental conditions were [<i>E</i>]₀ = 50 nM and [TBC]₀ = 1 mM. <b>Inset.</b> Spectrophotometric recordings of the action of tyrosinase on TBC and D-Arb. The experimental conditions were [<i>E</i>]₀ = 20 nM, [TBC]₀ = 0.5 mM and [D-Arb]₀ = 0.4 mM. The spectrophotometric recordings were made every 60 seconds.</p

Chemical structures of β-Arb and D-Arb.

<p>Chemical structures of β-Arb and D-Arb.</p

Apparent inhibition of tyrosinase by D-Arb.

<p><b>A.</b> Representation of initial rate values of tyrosinase on L-tyrosine in the absence (●) and presence (▲) of D-Arb (0.2 mM). The increase of absorbance corresponding to the apparent formation of dopachrome was followed at 475 nm. The experimental conditions were [<i>E</i>]₀ = 90 nM and R = [L-dopa]₀ / [L-tyrosine]₀ = 0.042. <b>Inset.</b> Graphical representation of the Lineweaver–Burk equation to show the inhibition of the monophenolase activity of tyrosinase in the absence (●) and presence (▲) of D-Arb (0.2 mM). The experimental conditions were the same as in the main figure. <b>B.</b> Representation of initial rate values of tyrosinase on L-dopa in the absence (●) and presence (▲) of D-Arb (0.2 mM). The experimental conditions were [<i>E</i>]₀ = 60 nM. <b>Inset.</b> Graphical representation of the Lineweaver–Burk equation showing the inhibition of the diphenolase activity of tyrosinase in the absence (●) and presence (▲) of D-Arb (0.2 mM). The experimental conditions were the same as in the main figure.</p

Potential of mean force (PMF) as a function of the z-distance between the carbon atoms at <i>para</i> position of <i>o</i>-diphenols.

<p>(A) Surface representation of the localization of ligand in the binding cavity of metatyrosinase. (B) Potential of mean force curves for β-ArbOH (solid line) and D-ArbOH (dashed line).</p

Kinetic constants for the characterization of the activity of tyrosinase on D-Arb and β-Arb and chemical shift values of carbon with the phenolic hydroxyl group.

<p>Kinetic constants for the characterization of the activity of tyrosinase on D-Arb and β-Arb and chemical shift values of carbon with the phenolic hydroxyl group.</p

Type and kinetic constants for the apparent inhibition of tyrosinase by D-Arb and β-Arb.

<p>Type and kinetic constants for the apparent inhibition of tyrosinase by D-Arb and β-Arb.</p

Schematic representation of the action mechanism of tyrosinase on D-Arb.

<p>D-Arb = deoxyarbutin, D-ArbOH = hydroxylated deoxyarbutin, P = quinone derived from hydroxylated deoxyarbutin, <i>E</i>_m = metatyrosinase, <i>E</i>_d = deoxytyrosinase and <i>E</i>_ox = oxytyrosinase.</p

Computational results for the <i>oxy</i> form of mushroom tyrosinase (<i>Agaricus bisporus</i>).

<p>A representative MD snapshot is shown for the configurations of β-arbutin (A) and deoxyarbutin (B) in the active centre. The atom colours are as follows: red = oxygen, blue = nitrogen, light blue (spheres) = copper, green = carbon and white = hydrogen. In yellow dashed lines: possible hydrogen bonds interactions. Only the most relevant residues are depicted.</p