BETA-GLUCOSYLATION OF PLANT PHENOLICS BY PHENOL BETA-GLUCOSYLTRANSFERASE IN LARVAL TISSUES OF THE TOBACCO HORNWORM, MANDUCA-SEXTA (L)

Activity of phenol beta-glucosyltransferase (PGT) in labial gland and fat body tissue preparations from feeding 5th stadium larval tobacco hornworms, Manduca sexta, towards a variety of plant phenolics was determined by HPLC analysis of the beta-glucoside products formed. The enzymes in the 15,000 g fractions of tissue homogenates with uridine 5'-diphosphoglucose as a cofactor showed a wide range of activity in conjugating simple mono-, di-, and triphenols; phenolic acids, aldehydes, and alcohols; and coumarins and flavonoids. Highest specific activity of both labial gland and fat body enzyme preparations occurred with diphenol substrates such as catechol, hydroquinone, and vanillin, whereas lowest activities generally were observed with flavonoid substrates. The labial gland PGT had higher specific activity for the simple phenolic substrates than did the fat body enzyme. However, the coumarins and flavonoids were glucosylated at nearly the same rates by both enzyme preparations. Although the functions of PGT in labial glands and fat body are unknown, evidence from this study suggests that they could be important in conjugating a number of potentially toxic plant phenols occurring in the larval diet.