The Binding Affinity of Small Molecules with Yam Tyrosinase (Catechol Oxidase): A Biophysical Study.

Tabassum Mulla,Sushama Patil,Jyoti Jadhav,Srinivas Sistla

doi:10.1155/2019/8284968

Abstract

Yam tyrosinase has become an economically essential enzyme due to its ease of purification and abundant availability of yam tubers. However, an efficient biochemical and biophysical characterization of yam tyrosinase has not been reported. In the present study, the interaction of yam (Amorphophallus paeoniifolius) tyrosinase was studied with molecules such as crocin (Crocus sativus), hydroquinone, and kojic acid. Surface plasmon resonance (SPR), fluorescence spectroscopy, and circular dichroism techniques were employed to determine the binding affinities and the changes in secondary and tertiary structures of yam tyrosinase in the presence of four relevant small molecules. Hydroquinone and crocin exhibited very low binding affinities of 0.24 M and 0.0017 M. Due to their apparent weak interactions, competition experiments were used to determine more precisely the binding affinities. Structure-function interrelationships can be correlated in great detail by this study, and the results can be compared with other available tyrosinases.

Highlights

Tyrosinase is a universal enzyme present in all living organisms
The tyrosinases of plants are involved in the synthesis of phenolic polymers like lignin, flavonoids, and tannins and are involved in some metabolic processes such as cellular respiration, regulation of oxidation-reduction potential, host defense, and wound healing [2, 3]. e lack of tyrosine hydroxylation is a distinct feature of plant tyrosinase compared to animal tyrosinases
Tyrosinase leads to undesirable browning during the processing of fruits and vegetables and reduces their commercial value. erefore, tyrosinase inhibitors have been under study for some time, and the use of these inhibitors has increased in the cosmetic, medicinal, and food industries [4, 5]

Summary

Introduction

Tyrosinase is a universal enzyme present in all living organisms. It is involved in the conversion of monophenols to diphenols by monophenolase activity and further conversion of diphenols into quinones by diphenolase activity. Tyrosinases and catecholamines (neurotransmitters synthesized by hydroxylation of tyrosine by the action of tyrosine hydroxylase) differ in a single amino acid, G241. Understanding these differences between plant and animal enzymes will help designing effective modulators. Patil et al [13] used the SPR system for studying the binding events between mushroom tyrosinase and small molecules. A competitive analyte kinetics model approach was conducted to study the interactions between inhibitors like kojic acid, hydroquinone, and crocin towards yam tyrosinase. E strategy of using a combination of (inhibitors) kojic acid, hydroquinone, and crocin along with its substrate, L-DOPA was to study the binding and synergistic effect of these molecules with immobilized yam tyrosinase. The effect of small molecules on yam tyrosinase was determined with fluorescence spectroscopy and circular dichroism (CD) spectroscopy techniques

Materials and Methods

Enzyme Activity Assay

Results and Discussion