Dual effects of aliphatic carboxylic acids on cresolase and catecholase reactions of mushroom tyrosinase

Figures & data

Figure 1.  Structures of aliphatic acids as inhibitors of MT.

Figure 2.  MT activation in the catecholase reactions with MeBACat as substrate in 10 mM PBS, 20 °C and pH 6.8, in the presence of pyruvic acid (○), acrylic acid (♦), propanoic acid (▵), 2-oxo-butanoic acid (□) and 2-oxo-octanoic acid (◊).

Table 1.  Activation and inhibition parameters in catecholase and cresolase reactions

	Catecholase reactions		Cresolase reactions
	Maximum R.A.(%)	Optimum A.C. (mM)	Ki (mM)	Inhibition mode
Pyrovic acid	215	1	0.36	competitive
Acrylic acid	342	1.25	0.6	competitive
Propanoic acid	245	2	0.14	uncompetitive
2-Oxo-butanoic acid	140	2.2	3.6	competitive
2-Oxo-octanoic acid	163	3.2	4.5	competitive

R.A.: Relative Activity; A.C.: Activity concentration; K_i: Inhibition constant

Figure 3.  (a) Double reciprocal Lineweaver-Burk plots of MT kinetic assays for cresolase reactions with MePAPh in 10 mM PBS, 20 °C and pH 6.8, in the presence of different fixed concentrations of propanoic acid: 0 (♦), 0.5 (□), 1.0 (▴), 1.25 (×) and 1.5 mM (*). (b) The secondary plot of reciprocal apparent maximum velocity (1/ V′_max) versus the concentration of inhibitor [I], where the abscissa-intercept is −K_i.

Figure 4.  Double reciprocal Lineweaver-Burk plots of MT kinetic assays for cresolase reactions with Me-PAPh in 10 mM PBS, 20 °C and pH 6.8, in the presence of different fixed concentrations of 0 (♦), 0.1 (□), 0.2 (▴), 0.4 (×) and 0.75 mM (*) for pyruvic acid (a); 0 (♦), 0.2 (□), 0.4 (▴), 0.8 (×) and 1.2 mM (*) for acrylic acid (b); 0 (♦), 0.4 (□), 1 (▴), 1.5 (×) and 2.5 mM (*) for 2-oxo-butanoic acid (c) and 0 (♦), 0.5 (□), 1 (▴), 1.5 (×) and 2 mM (*) for 2-oxo-octanoic acid (d).

Figure 5.  The secondary plots of the slopes for the lines in Figure 4 (a–d) against the concentration of inhibitor, [I], gives a straight line with an abscissa intercept of inhibition constant (−K_i) for pyruvic acid (a), acrylic acid (b), 2-oxo-butanoic acid (c) and 2-oxo-octanoic acid (d).