Chemical Reaction Catalyzed

LGTase catalyzes the glucosylation of limonoid agly-cones to form their respective 17ft-D-glucopyranoside derivatives (12-14). Seventeen limonoid glucosides have been isolated from Citrus and its closely related genera (15). Each has a single glucose molecule attached to the 17-position of the limonoid molecule via a ft-glu-cosidic linkage, such as limonin 17ft-D-glucopyranoside (Fig. 1). The isolated enzyme from the albedo tissues of navel oranges takes both limonoate A-ring lactone and nomilinoate A-ring lactone as its substrates (13). This indicates that the enzyme is able to convert all limonoid aglycones present in Citrus sp. to their respective gluco-sides. Southern blot analysis of genomic DNA supports this observation—the gene for this enzyme is present only as a single copy in the citrus genome (16).

Figure 1 Mechanism of delayed bitterness in extracted citrus juice and the mechanism of glucosylation (a naturally occurring limonin debittering process) in Citrus.
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