Isolation and partial characterization of phenol oxidases from Mangifera indica L. sap (latex)

Mango sap (latex), a by-product in mango industry, was separated into upper non-aqueous phase and lower aqueous phase. Aqueous phase contains very low protein (4.3 mg/ml) but contains high specific activities for peroxidase and polyphenol oxidase. The aqueous phase of sap was subjected to ion-exchange chromatography on DEAE-Sephacel. The bound protein was separated into three enzyme peaks: peak I showed peroxidase activity, peak II showed polyphenol oxidase activity and peak III showed activities against substrates of peroxidase as well as polyphenol oxidase. On native PAGE and SDS-PAGE, each peak showed a single band. Based on the substrate specificity and inhibitor studies peak III was identified as laccase. Although they showed variations in their mobility on native PAGE, these enzymes showed similar molecular weight of 100,000 ± 5000. These enzymes exhibited maximum activity at pH 6 however, polyphenol oxidase showed good activity even in basic pH. Peroxidase and polyphenol oxidase showed stability up to 70 °C while laccase was found to be stable up to 60 °C. Syringaldazine was the best substrate for laccase while catechol was the best for polyphenol oxidase. Thus, mango sap a by-product in mango industry is a good source of these phenol oxidases.