Bioconversion of Gentisein to Norathyriol by <i>Mangifera indica</i> L. Leaf Cell-Free Extract

Mangifera indica (mango) leaves are a source of bioactive xanthones—including mangiferin, gentisein, and norathyriol—that possess hypoglycemic, anti-cancer, and antioxidant activities. The co-occurrence of these structurally related compounds suggests the presence of enzymes involved in their biosynthesis in the mango leaves. For the synthesis of bioactive compounds using cell-free extracts, the catalytic activities of the enzymes involved in the proposed biosynthetic pathway should be determined. This study aimed to investigate the hydroxylase activity that converts gentisein to norathyriol, and the C-glycosidase activity that cleaves mangiferin to norathyriol in the mango leaf cell-free extract. The enzymatic products were detected via high-performance liquid chromatography. The results indicated the presence of norathyriol with an enzymatic activity of 3.89 µmoles/min/mg protein (64.83 nkat/mg protein) using gentisein as a substrate. The change in the peak area for mangiferin in the reaction was also presented. These results demonstrated that the enzymatic functions in the mango leaves extract catalyzed gentisein to norathyriol. Consequently, a potential strategy can be inferred for developing a biocatalytic process of norathyriol production.