Role of prolyl endopeptidase in intracellular transport and protein secretion.

Prolyl endopeptidase (E.C. 3.4.21.26, PREP) also known as prolyl oligopeptidase is an enzyme which cleaves several peptides at the carboxyl side of proline residues. Since brain contains relatively large amounts of this enzyme and because of its substrate specificity it has been suggested to play a role in the metabolism of neuropeptides, acting both on their maturation and their degradation. The final step of neuropeptide processing occurs in the synaptic vesicles and degradation of most of these peptides takes place in the synaptic cleft. Thus, a localization of PREP in these cellular compartments appears to be feasible. Here we summarize recent data and provide novel evidence for the subcellular localization of PREP. Most importantly, immunocytochemical double labelling, confocal laser scanning and electron microscopic procedures as well as functional assays strongly suggest a role for PREP in intracellular transport mechanisms and in protein secretion.