Cloning and sequence analysis of cDNA for bovine carboxypeptidase E

Carboxypeptidase E (enkephalin convertase) was first identified as the carboxypeptidase B-like enzyme involved in the biosynthesis of enkephalin in bovine adrenal chromaffin granules¹. A similar enzyme is present in many brain regions^1,2 and in purified secretory granules from rat pituitary³ and rat insulinoma⁴. Within the secretory granules, carboxypeptidase E (CPE) activity is found in both a soluble and a membrane-bound form¹, which differ slightly in relative molecular mass (M_r)⁵. Here, to investigate whether the CPE activities in the various tissues are produced from a single gene, purified CPE was partially sequenced and oligonucleotide probes were used to isolate a clone encoding CPE from a bovine pituitary complementary DNA library. This cDNA hybridizes to bovine pituitary poly(A)⁺ RNAs of approximately 3.3, 2.6 and 2.1 kilobases (kb), with the 3.3-kb messenger RNA the predominant species. The predicted amino-acid sequence of the cDNA clone contains the partially determined sequences of CPE, several pairs of basic amino acids and displays some homology with both carboxypeptidases A and B. Restriction analysis of bovine genomic DNA suggests only one gene for CPE. This is consistent with a broad role for CPE in the biosynthesis of many neuropeptides.