Converts proline to delta-1-pyrroline-5-carboxylate. 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. Repressed by FadR in the absence of LCFAs (fatty acids of 14-20 carbon atoms). When LCFAs are present in the medium, they are converted to long-chain acyl-CoAs, which antagonize fadR as to its binding to fadR boxes on target DNA and thus derepress transcription. Belongs to the proline dehydrogenase family.