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 Optimum pH is 8.2. 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 (By similarity). Interacts with GRF3. Expressed in roots. Expressed at low level in flowers and siliques. By indole-3-acetic acid (IAA) and cycloheximide (CHX). 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.