Biochemistry

Plants produce a vast array of natural compounds. Many of them are not commercially available, and are thus lacking to be tested as substrates for enzymes. This protocol describes the extraction and acidic hydrolysis of metabolites from Barbarea vulgaris with special focus on saponins and their agylcones (sapogenins). It was developed to determine if some B. vulgaris UDP-glucosyltransferases (UGTs) that were shown to glucosylate commercially available sapogenins, would also accept additional sapogenins from this plant as substrate, which are yet chemically uncharacterized and/or commercially unavailable (Figure 1).


Figure 1. Glucosylation reaction catalyzed by UGT73C10-UGT73C13 from Barbarea vulgaris (Augustin et al., 2012). All four enzymes utilize uridine diphosphate glucose (UDP-glc) as glucosyl-moiety donor and different sapogenins such as the oleanane sapogenins oleanolic acid and hederagenin as glucosyl-moiety acceptor. Oleanolic acid and hederagenin both naturally occur in G-type B. vulgaris, where they are predominantly found in their 3-O-cellobiosylated form. Additional saponins from G-type B. vulgaris have been identified by Nielsen et al., 2010. However, the majority of saponins and sapogenins that occur in B. vulgaris remain unidentified.