The regulation of the putBCP operon. The operon is activated by both the presence of proline and putR (Proline-responsive transcriptional activator). Therefore, the operon is inhibited by the absence of proline. The operon can also be inhibited by high concentration of proline due to the cell protecting itself from high osmolarity. Proline is brought into the cell by the putP (High-affinity proline transporter) and opuE (Osmoregulated proline transporter) transporters. When proline is present in the cell, putR binds to the promoter which is essential for the transcription of the operon. When proline is absent or in high concentration, putR releases the promoter inhibiting the transcription of the operon. There are three products of this operon: putB (Proline dehydrogenase 2), putC (1-pyrroline-5-carboxylate dehydrogenase 2) and putP. PutP is a transporter used in proline transportation into the cell. PutB and putC are enzymes used to turn proline into glutamate. PutB turns proline into 1-pyrroline-5-carboxylate. 1-pyrroline-5-carboxylate spontaneously changes to L-glutamate 5-semialdehyde with the addition of water. The reverse also occurs spontaneously with the removal of water. PutC turns L-glutamate 5-semialdehyde to glutamate.

Proline utilization: putB, putC, putP References