Neuropeptide processing by single-step cleavage: conversion of leumorphin (dynorphin B-29) to dynorphin B

Dynorphin B (rimorphin) is formed from dynorphin B-29 (leumorphin) by the action of a thiol protease from rat brain membranes. This represents a "single-arginine cleavage" between threonine-13 and arginine-14 of the substrate. In isotope dilution experiments we find that the radioactivity from radiolabelled dynorphin B-29, which appears in dynorphin B during incubation with the enzyme preparation, is not diminished by addition of a high concentration of dynorphin B-Arg14. Moreover, in pulse-chase experiments, radioactivity that appeared in dynorphin B-Arg14 did not decrease, nor did the radioactivity in dynorphin B increase, after chasing with a high concentration of non-radioactive dynorphin B-29. These results indicate that although some dynorphin B-Arg14 is formed by the impure enzyme preparation, it is not an intermediate in the conversion of dynorphin B-29 to dynorphin B. Thus the formation of dynorphin B does not involve the action of a trypsin-like enzyme followed by removal of arginine-14 by a carboxypeptidase B-like enzyme. It appears that a single enzyme converts dynorphin B-29 to dynorphin B in a single step.