Characterization of Aplysia carboxypeptidase E

Carboxypeptidase E (CPE) is involved in the biosynthesis of peptide hormones and neurotransmitters. To determine whether a recently reported Aplysia californica cDNA encodes a CPE‐like enzyme, this cDNA was expressed in the baculovirus system. The Aplysia CPE is optimal at pH 5.5–6.5 and is inhibited by chelating agents and by the sulfhydryl reagent p‐chloromercuriphenyl sulfonate. The effect of divalent cations and active site‐directed inhibitors on enzyme activity are generally similar for Aplysia and rat CPE. Western blot analysis using antisera to the N‐ and C‐terminal regions of the Aplysia CPE show that the Aplysia CPE is present in atrial glands and ovotestis. This Aplysia CPE is purified on a p‐aminobenzoyl–Arg Sepharose affinity column under conditions that selectively purify rat CPE. Taken together, these results suggest that the previously cloned cDNA represents a CPE‐like enzyme that is expressed in Aplysia tissue.