Tyrosinase (E.C. 1.14.18.1), a copper containing oxidase, is responsible for catalyzing the first steps of the melanin formation pathway. In our search for plant derived tyrosinase inhibitors, benzaldehydes sourced from African medicinal plants were explored. 2-hydroxy-4-methoxybenzaldehyde (HMB) was reported to inhibit the tyrosinase-catalyzed oxidation of L-3,4-dihydroxyphenylalanine (L-DOPA) and was also able to suppress melanogenesis activity. The mechanism behind tyrosinase suppression has not been well understood. In cell free experiments, it is likely that HMB aldehyde group forms a Schiff base with the primary amino acid group on the enzyme. The hydroxyl and methoxy groups then contribute by stabilizing a newly formed ring complex that suppresses the enzyme. To better understand the mechanisms behind this activity the structurally similar compound isovanillin (3-hydroxy-4-methoxybenzaldehyde) was explored. Instead of using L-DOPA as a substrate, L-Tyrosine was tested as it is the natural substrate that begins this pathway. When enzyme activity was monitored by measuring the oxidation of L-Tyrosine to dopachrome spectrophotometrically isovanillin showed the same suppression activity as HMB. Yet, isovanillin has a hydroxyl group in the met position so no ring could be formed and the aldehyde group alone could not be the only source of suppression. Thus the focus went to the hydroxyl group and the redox-reaction ability of isovanillin was investigated which was key to understanding isovanillins ability to suppress dopachrome formation.

Mechanisms behind benzaldehyde suppression of the enzyme tyrosinase

251st National Meeting (2016)

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