Dual activities of ACC synthase: Novel clues regarding the molecular evolution of genes.

Ethylene plays profound roles in plant development. The rate-limiting enzyme of ethylene biosynthesis is 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS), which is generally believed to be a single-activity enzyme evolving from aspartate aminotransferases. Here, we demonstrate that, in addition to catalyzing the conversion of -adenosyl-methionine to the ethylene precursor ACC, genuine ACSs widely have C-S lyase activity.