Hen egg white lysozyme as an inhibitor of mushroom tyrosinase

Abstract 

We report a kinetics study on hen egg white lysozyme’s (HEWL) inhibitory effect on mushroom tyrosinase catalysis of 3-(3,4-dihydroxyphenyl)-l-alanine (l-DOPA) or l-tyrosine. For the first time, we demonstrate HEWL as a robust inhibitor against mushroom tyrosinase in catalysis of both substrates. The kinetics pattern matches a mixed (mostly non-competitive) partial inhibition. K_i and ID₅₀ value of HEWL are more than 20-fold lower than that of kojic acid, a well-known chemical inhibitor of mushroom tyrosinase. K_i, α value and β value, are almost identical in both experiments (l-DOPA and l-tyrosine as substrates, respectively), which suggests this common inhibition mechanism affects both steps. The inhibitory effect increases as both proteins were mixed and pre-incubated for less than 1h. HEWL-depletion only removed about half of the inhibitory effect. Here we propose a novel function of HEWL, which combines the reversible inhibition and the irreversible inactivation toward mushroom tyrosinase. Discovery of HEWL as an inhibitor to mushroom tyrosinase catalysis may be commercially valuable in the food, medical and cosmetic industries.

Abbreviations: HEWL, hen egg white lysozyme, l-DOPA, 3-(3,4-dihydroxyphenyl)-l-alanine

Keywords: Antibacterial protein, Muramidase, Kojic acid, Peptidoglycan N-acetylmuramoylhydrolase, EC 3.2.1.17, Monophenol, dihydroxy-l-phenylalanin: oxygen oxidoreductase, EC 1.14.18.1