Comprehensive kinetic and structural studies of different flavonoids inhibiting diphenolase activity of mushroom tyrosinase

The effect of 4 flavonoids on the diphenolase activity of mushroom tyrosinase was studied using spectroscopic approach. Analysis of kinetic data demonstrated that flavonoids cause a reversible inhibition of the enzyme activity. Further study showed that gallic acid acted as noncompetitive inhibitor, whereas chrysin, naringin and quercetin inhibited the diphenolase activity of mushroom tyrosinase in a competitive fashion. Comparison of the inhibition constants revealed that the strength with which the inhibitors acted on the enzyme activity was ranking as follows: chrysin ( K i 7.90 mM) < quercetin ( K i 7.44 mM) < naringin ( K i 3.04 mM) < gallic acid ( K i 1.5 mM). These data, therefore, suggest that gallic acid is the most potent inhibitor of the enzyme compared to the other flavonoids used.