Study on the interaction of kojic acid with tyrosinase by spectroscopic methods

Abstract

Tyrosinase is the key enzyme in melanin synthesis, and kojic acid is a widely available inhibitor against tyrosinase with extensive application values. The inhibitory mechanism of kojic acid was elaborated by studying the mutual interaction and the effects on tyrosinase conformation using spectroscopy. Ultraviolet-visible absorption spectra showed kojic acid caused both the secondary and tertiary structure changed. Fluorescence lifetime measurements implied that kojic acid quenched the intrinsic fluorescence of tyrosinase via static process. A complex formed through one single binding site with a binding constant of 1.35×105 M-1 . Thermodynamic parameters suggested that the binding was a spontaneous process with hydrogen bonds and van der Waals forces playing main role. Synchronous fluorescence spectra and three-dimensional fluorescence spectra showed that kojic acid induced obvious conformational changes in tyrosinase and increased the polarity of microenvironment. Circular dichroism revealed an increase of the content of α-helix and β-strand. This study will provide reliable basis concerning the inhibitory mechanism of kojic acid against tyrosinase, and therefore contribute to development of tyrosinase inhibitor.