Converts proline to delta-1-pyrroline-5-carboxylate. Important for the use of proline as a sole carbon and energy source or a sole nitrogen source. a quinone + L-proline = (S)-1-pyrroline-5-carboxylate + a quinol + H(+) Amino-acid degradation; L-proline degradation into L-glutamate; L-glutamate from L-proline: step 1/2. The expression of the putBCP operon is induced in a PutR-dependent fashion by very low concentrations of L-proline in the growth medium. CodY represses the operon by displacing PutR from DNA. Deletion of the putBCP operon abolishes L-proline utilization. Belongs to the proline dehydrogenase family.