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. By wounding in fruit and etiolated hypocotyls. By indoleacetic acid (IAA)/benzyladenine/LiCl only in fruit tissue. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.