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 7.8. 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 (via its C-terminal region) with FEI1, FEI2, ETO1, EOL1 and EOL2 (PubMed:15118728, PubMed:19017745, PubMed:18808454). Interacts with GRF3 (PubMed:25122152). Expressed in roots and siliques. By indole-3-acetic acid (IAA) and cycloheximide (CHX). In response to low dose of cytokinin. May be processed at its C-terminus. Ubiquitinated (Probable). The interaction with ETO1 (and possibly EOL1 and EOL2) mediate its proteasome-dependent degradation. Its stability and degradation plays a central role in ethylene biosynthesis. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.