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. 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 XBAT32. Expressed in roots. By cycloheximide (CHX). Ubiquitinated by XBAT32. Ubiquitination probably leads to its subsequent degradation, thus controlling ethylene production. 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.