Biosynthesis of naringin in Citrus paradisi: UDP-glucosyl-transferase activity in grapefruit seedlings

Abstract

A UDP-glucosyltransferase activity capable of position-specific transfer of glucose to the 7-position of naringenin has been isolated from grapefruit seedlings. Leaves are the richest source of this activity on a fresh weight basis. Characteristics include a pH optimum of 6.5–7.5, a temperature optimum of 37°, an apparent E act of 7.76 kcal mol −1, and an apparent K m for naringenin of 0.08 mM. Hesperitin and 2′,4′,6′,4-tetrahydroxychalcone are also glucosylated with apparent K m 's of 0.11 mM and 0.13 mM respectively. Thermal degradation studies indicate that the naringenin and hesperitin glucosylating activities have different stabilities. Chromatofocusing resolves the naringenin glucosylating activity into two peaks with apparent pI's of 4.4 and 3.9. The hesperitin glucosylating activity separates into three peaks with apparent pI's of 4.5, 4.4, and 4.0.