Bovine pancreatic procarboxypeptidase A has been overexpressed in a soluble and activatable form in Escherichia coli. When the protein was expressed under the control of bacteriophage T7 promoter in E coli ADA494 (a thioredoxin reductase deficient bacteria), a thioredoxin fusion protein was produced at relatively high level in the cytoplasm (4 mg/L culture medium). Although the recombinant protein essentially accumulated as inclusion bodies, as much as 30% of the fusion protein was recovered in a soluble form at low growth temperature and could therefore be purified to homogeneity in a single-step procedure by metal-affinity chromatography. The recombinant precursor form of bovine carboxypeptidase A was recognized by a monoclonal antibody directed against purified bovine pancreatic carboxypeptidase A. Moreover, upon tryptic activation it gave rise to an enzyme, the N-terminal sequence, molecular size,and specific activity of which were comparable to those of the enzyme derived from the native precursor purified from bovine pancreas. (C) 2002 Elsevier Science (USA). All rights reserved.