It is found that catechol inhibits the oxidase-mimicking activity of chitosan-protected platinum nanoparticles (Chit-PtNPs) by competing with the substrate for the active site of the Ch-PtNPs. The inhibition mechanism of catechol is different from that of ascorbic acid in that it neither reacts with O2•- nor reduces the oxidized 3,3',5,5'-tetramethylbenzidine (TMB). Tyrosinase (TYRase) catalyzes the oxidation of catechol, thus restoring the activity of oxidase-mimicking Chit-PtNPs. By combining the Chit-PtNP, catechol, and TYRase interactions with the oxidation of TMB to form a yellow diamine (maximal absorbance at 450 nm), a colorimetric analytical method was developed for TYRase determination and inhibitor screening. The assay works in the 0.5 to 2.5 U·mL-1 TYRase activity range, and the limit of detection is 0.5 U·mL-1. In our perception, this new assay represents a powerful approach for determination of TYRase activity in biological samples. Graphical abstract Schematic representation of a colorimetric method for tyrosinase (TYRase) detection and inhibitor screening. It is based on the fact that catechol can inhibit the oxidase-like activity of chitosan-stabilized platinum nanoparticles (Ch-PtNPs) by competing with the substrate for the active sites and TYRase can catalyze the oxidation of catechol.
Keywords: Enzyme mimetic; Inhibitory effect; Kojic acid; Oxidase-like activity; Tetramethylbenzidine; o-Quinone.