Fig. 3

QA biosynthetic pathway in NLL and classification of QAs into core and esterified QAs. QAs are synthesized from l-lysine, which is decarboxylated by LDC to yield cadaverine. In turn, cadaverine is oxidatively deaminated to ∆¹-piperideine by CAO. Three ∆¹-piperideine molecules are then joined to form a four-ring, putative di-iminium intermediate from which all core QAs are thought to be derived [40]. The simplest QAs that accumulate in NLL are lupanine and isolupanine. These two QAs can be converted to angustifoline and isoangustifoline via ring opening with loss of one carbon or to 13-hydroxylupanine and 13-hydroxyisolupanine via hydroxylation. Altogether, these six compounds constitute the main core QAs in NLL. Additionally, acyltransferases (ATs) can conjugate 13-hydroxylupanine to various acyl-CoA derivatives to form an array of esterified QAs. Abbreviations: LDC, lysine decarboxylase; CAO, copper amine oxidase; ATs, 13-hydroxylupanine O-acyltransferases. Plain and dashed arrows indicate, respectively, characterized and predicted steps. The (R) and (S) labels refer to the absolute configuration at the carbon atom marked with the wavy bond. ^†These isomers were analyzed together as a single compound. ^‡Only one of these isomer pairs accumulates in the leaves of NLL cv. Oskar; we did not determine which one