STRUCTURE, FUNCTION, AND REGULATION OF THE CHALCONE SYNTHASE

This chapter presents an overview of the activity, function, and control of chalcone synthase (CHS) enzyme. It describes the reaction it catalyzes, the secondary metabolic products of the pathways in which it is involved, and the functions of these products. The chapter also explores how CHS is regulated to facilitate flavonoid biosynthesis under particular developmental and environmental conditions. CHS is a condensing enzyme, unique to plants, that builds a 15-carbon (C15) intermediate from which all flavonoids are derived. It is regarded the key enzyme of flavonoid biosynthesis, as it is the first enzyme committed to flavonoid production. Because changes in the activity of CHS are closely associated with the induction of synthesis of many different flavonoids, it represents an enzyme under considerable environmental and developmental regulation. Chalcone synthase catalyzes the formation of naringenin chalcone from one molecule of 4-coumaroyl CoA and three molecules of malonyl CoA. The biosynthesis proceeds by stepwise decarboxylative condensation of acetate units from the malonyl residues with the starter 4-coumaroyl CoA residue, releasing four molecules of CoA and three of CO2 in the process. Very closely related to chalcone synthases are the enzymes that synthesize the backbone of the stilbene phytoalexins, the stilbene synthases (STS). © 1993, Elsevier Science Publishers, B.V.