1-aminocyclopropane-1-carboxylate synthase (ACS) enzymes catalyze the conversion of S-adenosyl-L-methionine (SAM) into 1-aminocyclopropane-1-carboxylate (ACC), a direct precursor of ethylene. S-adenosyl-L-methionine = 1-aminocyclopropane-1-carboxylate + H(+) + S-methyl-5'-thioadenosine Alkene biosynthesis; ethylene biosynthesis via S-adenosyl-L-methionine; ethylene from S-adenosyl-L-methionine: step 1/2. Homodimer and heterodimer. In vivo, the relevance of heterodimerization with other ACS enzymes is however unsure. Hormones, such as auxin, environmental factors, such as mechanical wounding and a number of chemicals. Phosphorylated on Ser 460; phosphorylation may regulate its turnover. May be processed at its C-terminus. The stability of ACS proteins, and the regulation of such stability, play a central role in ethylene biosynthesis. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.