Substituent effect of benzaldehydes on tyrosinase inhibition.

Benzaldehyde inhibited the oxidation of 4-t-butylcatechol catalyzed by mushroom tyrosinase with an IC of 31.0 μM. The inhibition kinetics analyzed by Dixon plot indicated that it acts as a partial noncompetitive inhibitor. Further studies of several benzaldehydes, particularly those having a substitution at C-4, suggested that the partial inhibitory property diminished when using a bulk substituent. For example, 4-penthylbenzaldehyde showed a full and mixed type inhibition on diphenolase activity. Therefore, 4-substituted benzaldehyde on the aromatic ring primarily reflected the rate of product formation as it may act as a tight hydrophobic cover on the catalytic center of tyrosinase.