Purification and characterization of the Manduca sexta neuropeptide processing enzyme carboxypeptidase E

The neuropeptide processing enzyme carboxypeptidase E (CPE) (E.C.3.4.17.10) has been well studied in vertebrates but its presence in invertebrates has not yet been reported. CPE activity in insects is present in membrane-bound and soluble forms. The soluble CPE has been purified to homogeneity from the brain of the tobacco hornworm Manduca sexta. It is a 57 kDa glycoprotein containing 9% sugars. It is activated 9.2 +/- 1.8 fold by CoCl2 and inhibited by chelating agents. Its sensitivity to guanidinoethyl-mercaptosuccinic acid, and its molecular mass, make this enzyme a good candidate to be the insect equivalent of the mammalian CPE. Furthermore, its lack of sensitivity towards p-(chloromercuri)benzenesulfonate puts it closer to the vertebrate carboxypeptidase M (CPM). We postulate that insects may possess a single protein fulfilling both CPE and CPM functions.