(Met)enkephalin and carboxypeptidase processing enzyme are co-released from chromaffin cells by cholinergic...

A carboxypeptidase B-like enzyme is involved in processing of proenkephalin in adrenal medulla. Nicotine stimulated the co-release of this enzyme with (Met)enkephalin pentapeptide from bovine chromaffin cells in primary culture. The ratio of enzyme activity/immunoreactivity was determined for the released carboxypeptidase to provide an index of the level of enzyme activity per unit number of enzyme molecules. The ratio for the Co++-stimulated carboxypeptidase secreted into the cell culture medium upon nicotinic stimulation was 10.1 +/- 1.02 (pmol Met-enkephalin formed per ng carboxypeptidase immunoreactivity), while the Co++-stimulated carboxypeptidase in the soluble and membrane components of purified chromaffin granules had lower ratios of 5.46 +/- 0.70 and 1.07 +/- 0.13, respectively. Hexamethonium, a nicotinic receptor antagonist, blocked the nicotine-induced release of the carboxypeptidase processing enzyme and (Met)enkephalin. These data suggest that a pool of carboxypeptidase enzyme molecules at a high state of activation are present in functionally mature granules whose contents are released by nicotinic receptor stimulation.