Immunochemical characterization of carboxypeptidase B-like peptide-hormone-processing enzyme.

Specific rabbit antisera against purified bovine pituitary carboxypeptidase processing enzyme (which has also been referred to as "enkephalin convertase") have been prepared and characterized. The antisera recognized both the purified soluble and the membrane-bound forms of the enzyme with equal affinity, suggesting that these two forms of the enzyme may possess many regions of structural homology. Since the antisera did not crossreact with carboxypeptidases B, N, A, Y, and P, the carboxypeptidase processing enzyme may be a structurally distinct form of carboxypeptidase. Carboxypeptidase immunostaining, as seen by light microscopy, was found throughout the rat brain and in bovine adrenal medulla, reflecting the widespread distribution of neuropeptides. Electron microscopic immunocytochemistry of rat paraventricular nucleus and other brain areas showed that the enzyme was present in some dendrites and nerve terminals, which contain storage vesicles. These findings support the hypothesis that this carboxypeptidase is involved in the processing of many peptide hormone precursors.