Catalyzes the decarboxylation of S-adenosylmethionine to S-adenosylmethioninamine (dcAdoMet), the propylamine donor required for the synthesis of the polyamines spermine and spermidine from the diamine putrescine. Has no arginine decarboxylase (ArgDC) activity. H(+) + S-adenosyl-L-methionine = CO2 + S-adenosyl 3-(methylsulfanyl)propylamine Binds 1 pyruvoyl group covalently per subunit. Competitively inhibited by methylglyoxal bis-guanylhydrazone. Irreversibly inhibited by NaBH(4) in vitro. Optimum pH is 7.4. Optimum temperature is 75 degrees Celsius. Thermostable. Retains 20% activity after incubation at 100 degrees Celsius for 1 hour, 80% after 16 hours at 70 degrees Celsius, while no loss of activity is observed after 16 hours at 50 degrees Celsius. Amine and polyamine biosynthesis; S-adenosylmethioninamine biosynthesis; S-adenosylmethioninamine from S-adenosyl-L-methionine: step 1/1. Heterotetramer of two alpha and two beta chains arranged as a dimer of alpha/beta heterodimers. Is synthesized initially as an inactive proenzyme. Formation of the active enzyme involves a self-maturation process in which the active site pyruvoyl group is generated from an internal serine residue via an autocatalytic post-translational modification. Two non-identical subunits are generated from the proenzyme in this reaction, and the pyruvate is formed at the N-terminus of the alpha chain, which is derived from the carboxyl end of the proenzyme. The post-translation cleavage follows an unusual pathway, termed non-hydrolytic serinolysis, in which the side chain hydroxyl group of the serine supplies its oxygen atom to form the C-terminus of the beta chain, while the remainder of the serine residue undergoes an oxidative deamination to produce ammonia and the pyruvoyl group blocking the N-terminus of the alpha chain. Pyruvoyl group-containing alpha subunit. A chimeric protein containing the beta subunit of SSO0536 and the alpha subunit of SSO0585 (SpeH) has ArgDC activity and no AdoMetDC activity, implicating residues responsible for substrate specificity in the beta subunit. But additional factors in the alpha subunit are required for efficient cleavage and turnover. Belongs to the prokaryotic AdoMetDC family. Type 1 subfamily.