Schematic presentation of the three L-arginine-degrading pathways in Synechocystis sp. PCC 6803 with the corresponding enzymes, intermediates, cofactors, and final products. A). L-arginine decarboxylase pathway most likely only provides polyamines and ammonia. B) L-arginine deiminase pathway degrades L-arginine via L-citrulline to L-ornithine and carbamoyl phosphate. L-ornithine is further metabolized via glutamate semialdehyde to L-glutamate. Glutamate semialdehyde can also be converted to L-proline via Δ1pyrroline-5-carboxylate. Carbamoyl phosphate is further metabolized to ammonium and carbon dioxide. This enzymatic reaction is catalyzed by the enzyme carbamate kinase and is coupled to ATP synthesis. C) The L-arginine oxidase/dehydrogenase pathway converts L-arginine to succinate via 2-ketoarginine, 4-guanidinobutyrate, 4-aminobutyrate, and succinate semialdehyde.