. "C5H9NO2"^^ . "The zwitterion formed from L-proline by proton transfer from the carboxy group to the ring nitrogen. It is the predominant species at physiological pH."^^ . . . . . . "L-proline zwitterion"^^ . "(2S)-pyrrolidinium-2-carboxylate"^^ . "L-proline zwitterion"^^ . . . . . .