Converts proline to delta-1-pyrroline-5-carboxylate (PubMed:8096642). Involved in the conversion of proline to glutamate, which functions as transmitter at neuromuscular junctions (PubMed:8096642). Glutamate deficiency could possibly account for reduced motor activity (PubMed:8096642). 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. Most abundant in developing nervous system. Expressed in developing embryo as well as in adult. Flies exhibit reduced proline oxidase activity which produces sluggish behavior. Belongs to the proline oxidase family.