Figure 1

Biosynthesis of hop bitter acids from branched-chain amino acid (BCAA) precursors. a) The acyl side-chains of humulone/lupulone are derived from leucine, cohumulone/colupulone from valine and adhumulone/adlupulone from isoleucine via the corresponding acyl-CoA thioesters. The carbon chain of the BCAAs is shown in red to indicate their incorporation into the α- and β-acids. b) Schematic depiction of the major pathways contributing to the biosynthesis of the major α-acid product, humulone, in lupulin glands. Pathways are coloured to match Figure 2b: BCAA biosynthesis, purple; BCKDH complex, brown; MEP pathway, orange; malonyl-CoA biosynthesis, blue; bitter acid biosynthesis, green. The movement of metabolic intermediates between cellular compartments is indicated by dashed line. Note: the subcellular localization of the putative humulone synthase enzyme is not known.