Catalyzes the formation of 1-aminocyclopropane-1-carboxylate, a direct precursor of ethylene in higher plants (PubMed:17012402). Involved in defense response by producing ethylene at early stage after fungal pathogen infection (PubMed:17012402). Involved in several phospate deficiency-induced adaptive responses, such as lateral root elongation (PubMed:30810167). 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. Induced by partial submergence (PubMed:9037160). Induced in leaves by infection with the fungal pathogen Magnaporthe oryzae (PubMed:17012402). Induced by phosphate deficency (PubMed:30810167). Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.