Immunochemical characterization of a proline endopeptidase from rat brain. Its relationship to proline endopeptidase from other tissues and from other species.

Monospecific antiserum raised against rat brain proline endopeptidase is used to demonstrate the ubiquity of the enzyme and its unique role in the degradation of proline-containing peptides. All endoproteolytic activity directed toward proline residues in several rat tissues is shown to share one or more common antigenic determinants with rat brain proline endopeptidase. Similar activity from tissue of other species crossreacts with rat proline endopeptidase. The data presented suggest that proline endopeptidase is the sole cytoplasmic enzyme capable of degrading proline-containing peptides in every tissue examined and that previously reported proline-specific endoproteolytic activities observed in a variety of systems may be ascribed to proline endopeptidase. The putative role of proline endopeptidase in protein degradation is discussed.