Catalysis and inhibition of tyrosinase in the presence of cinnamic acid and some of its derivatives.

The kinetic action of tyrosinase on l-tyrosine and l-Dopa as substrates in the presence of cinnamic acid and some of its derivatives has been characterized. Cinnamic acid, 2-hydroxycinnamic, 2,3 and 4-methoxycinnamic acids were seen to be inhibitors of tyrosinase being determined the type of inhibition and inhibition constants of all of them. However, 3-hydroxycinnamic, 4-hydroxycinnamic and 3,4-dihydroxycinnamic acids were seen to be substrates of tyrosinase at the same time. The kinetic constants of the catalysis of these substrates were determined and found to be perfectly correlated with the chemical shifts of the carbon with the phenolic hydroxyl group revealed by NMR. Docking studies of 2-hydroxycinnamic and 3-hydroxycinnamic acids showed that tyrosinase is able to hydroxylate 3-hydroxycinnamic acid but is unable to hydroxylate 2-hydroxycinnamic acid.