DNA template-assisted inhibition of tyrosinase activity

Enzyme-mediated polymerization reactions have been widely studied in the context of DNA template-assisted reactions. We have recently highlighted the ability of DNA templates to modulate enzyme-catalyzed single-step transformations. In this work, we focus on the intramolecular transformation of L-dopa catalyzed by enzyme tyrosinase and report a novel role of DNA templates in inhibition of the enzyme. The kinetics of mushroom tyrosinase monitored by UV-visible spectroscopy reveals significant decrease in the enzyme's efficiency in the presence of short double-stranded DNA molecules. K<inf>M</inf> of tyrosinase is found to increase by nearly 1.8-fold, implying a lower affinity of the enzyme for L-dopa, whereas V<inf>max</inf> is only marginally affected. The mode of inhibition is assessed to be a mixed mode with kinetic constants of inhibition in the micromolar range. Further, in the presence of cinnamic acid and DNA duplexes, the K<inf>M</inf> of tyrosinase increases nearly 3.5-fold, whereas K<inf>i</inf> and K<inf>i</inf>' are lowered by an order of magnitude. These results are a corollary of the known influence of substrate-template interactions and greater local substrate concentrations on enzyme activity and expand the paradigm with respect to use of DNA templates in enzyme-catalyzed reactions.