Substrate specificity of chalcone synthase from Petroselinum hortense. Formation of phloroglucinol derivatives from aliphatic substrates.

The substrate specificity of chalcone synthase, the key enzyme of flavonoid biosynthesis, was investigated.A purified enzyme preparation from cell suspension cultures of parsley (Petroselinum hortense) catalyzed chain elongations with acetate units from malonyl-CoA, using various aromatic and aliphatic CoA esters as starter molecules.Malonyl-CoA could not be replaced by malonyl acyl carrier protein in the standard chalcone synthase assay.Butyryl-CoA, hexanoyl-CoA, and benzoyl-CoA served as substrates for the condensation reaction with similar efficiency as 4- coumaroyl-CoA, the natural substrate of the enzyme.Acetyl-coA and octanoyl-CoA were relatively poor substrates.Among the products formed with the two most efficient aliphatic substrates tested, butyryl-CoA and hexanoyl-CoA, were the respective chalcone analogues, phlorobutyrophenone and phlorocaprophenone.The possibility is discussed that chalcone synthase and the corresponding enzyme of fatty acid synthesis in higher plants, B-ketoacyl-acyl carrier protein synthase, have a common evolutionary origin.