TISSUE DISTRIBUTION OF A DYNORPHIN-PROCESSING ENDOPEPTIDASE

A number of peptide hormones and neurotransmitters require post-translational processing at monobasic cleavage sites. An enzymatic activity capable of processing prodynorphin at a monobasic processing site has been previously reported in rat brain and bovine pituitary. This dynorphin (Dyn)-converting enzyme (DCE) activity is capable of converting Dyn-B-29 (leumorphin) to Dyn-B-13 (rimorphin). The tissue distribution of the DCE activity in the adult rat shows that the activity is present at high levels in the brain, ileum, neurointermediate pituitary, and adrenal. Lower levels of activity are found in the anterior pituitary, liver, heart, ovary, kidney, lung, and serum. In the rat pituitary, the anterior lobe has 10-fold lower specific activity than the neurointermediate lobe. The protease inhibitor profile shows that the activity in various tissues is considerably inhibited by the thiol protease inhibitor p-chloromercuriphenyl sulfonic acid (PCMPS), suggesting that the Dyn-converting activity is due to a putative thiol protease. The Dyn-converting activity in the rat ileum and brain was subjected to ion exchange chromatography on diethylaminoethyl-cellulose; the majority of activity eluted around 0.3 M NaCl, as did bovine pituitary DCE. This chromatography behavior, peptide inhibitor profile, and pH optima are consistent with those of the previously reported enzyme activity from bovine pituitary and pituitary-derived cell lines. In the bovine brain, the distribution of activity generally matches that of Dyn-B-13. In the bovine adrenal medulla, the activity is localized to secretory vesicles that also contain carboxypeptidase-E activity, an enzyme thought to be involved with peptide processing. Taken together, the tissue distribution and enzyme properties support the possibility that the DCE is involved in the maturation of Dyn as well as many peptide hormones and neuropeptides.