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 with XBAT32. Interacts (via its C-terminal region) with ETO1 and EOL1. Expressed in roots, leaves and flowers. By indole-3-acetic acid (IAA) and cycloheximide (CHX). By auxin. 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.