Catalyzes the formation of 1-aminocyclopropane-1-carboxylate, a direct precursor of ethylene in higher plants. 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. Hormones, such as auxin, environmental factors, such as mechanical wounding and a number of chemicals. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.