Abstract
A rat brain membrane extract was shown to convert synthetic dynorphin B-29 (leumorphin) to dynorphin B [dynorphin B-29-(1-13), rimorphin]. This represents a single arginine cleavage at Thr-Arg at positions 13 and 14 of the substrate. The product was identified by immunoprecipitation with a highly specific dynorphin B antiserum and by coelution with radiolabeled dynorphin B on reversed-phase high-performance liquid chromatography. The converting activity exhibits a pH optimum of 8. It is inhibited by a thiol protease inhibitor but not by inhibitors of cathepsin B or of serine proteases. It is inhibited by dynorphin A but not by various dynorphin A fragments. The converting activity is due to a novel thiol protease distinct from any known protease believed to function in the processing of biologically active peptides.

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