Oxidation of baicalein by tyrosinase and by o-quinones

Inhibitive Mechanism of Loquat Flower Isolate on Tyrosinase Activity and Melanin Synthesis in Mouse Melanoma B16 Cells

“…The effect of LFP on the viability of mouse melanoma B16 cells was assessed by the CCK8 method (Figure 4A). Result showed that LFP solution at less than 200 μg/mL was non-toxic to the cells, with a survival rate more than 80% (Gasowska-Bajger & Wojtasek, 2023). However, the viability of the cells decreased in a dose-dependent manner as the concentration of LFP increased.…”

Reply letter to Dr. Wojtasek regarding: Oxidation of flavonoids by tyrosinase and by o-quinones–comment on "Flavonoids as tyrosinase inhibitors in in silico and in vitro models: basic framework of SAR using a statistical modelling approach” published by K. Jakimiuk, S. Sari, R. Milewski, C.T. Supuran, D. Söhretoglu, and M. Tomczyk (J Enzyme Inhib Med Chem 2022;37:427-436)

“…Responding to the observations made by Dr. Wojtasek, we would like to evidence the relevant differences between out experimental conditions 1 and those described in the papers by Dr. Wojtasek’s group 2 , 3 . In their experiments, Dr. Wojtasek and co-authors worked with the same substrate (DOPA) and inhibitor concentration, of 50 µM 2 , 3 .…”

“…Responding to the observations made by Dr. Wojtasek, we would like to evidence the relevant differences between out experimental conditions 1 and those described in the papers by Dr. Wojtasek’s group 2 , 3 . In their experiments, Dr. Wojtasek and co-authors worked with the same substrate (DOPA) and inhibitor concentration, of 50 µM 2 , 3 . In our study 1 , similar to many other publications in the field 4 , 5 , the concentration of DOPA (the enzyme substrate) was of 0.25 − 2 mM, which is 5–40 times higher than the one of the works by Gąsowska-Bajger and Wojtasek 2 , 3 , leading thus to a saturation of the tyrosinase active site with the substrate and not allowing a competition between the enzyme and the inhibitor (present at equimolar concentrations, as in the situation described in Dr. Wojtasek’s work 2 , 3 .…”

“…It may be possible that under the experimental circumstances used by Gąsowska-Bajger and Wojtasek 2 , 3 where the substrate and inhibitor concentrations were equivalent, a competition between the inhibitor and the substrate for binding within the enzyme active site may occur, which might induce inhibitor oxidation, as described by Gąsowska-Bajger and Wojtasek 2 , 3 . However, under conditions used in our experiments 1 , the substrate concentration was orders of magnitude higher than that of the inhibitor, making the oxidation unlikely, also because the enzyme active site was saturated with substrate (L-DOPA) 1 .…”

“…In their experiments, Dr. Wojtasek and co-authors worked with the same substrate (DOPA) and inhibitor concentration, of 50 µM 2 , 3 . In our study 1 , similar to many other publications in the field 4 , 5 , the concentration of DOPA (the enzyme substrate) was of 0.25 − 2 mM, which is 5–40 times higher than the one of the works by Gąsowska-Bajger and Wojtasek 2 , 3 , leading thus to a saturation of the tyrosinase active site with the substrate and not allowing a competition between the enzyme and the inhibitor (present at equimolar concentrations, as in the situation described in Dr. Wojtasek’s work 2 , 3 . Furthermore, these authors worked with an enzyme concentration of 55 EU/mL, whereas in our study 1 the tyrosinase concentration was of 250 EU/mL.…”