Carboxypeptidase T, an extracellular carboxypeptidase from Thermoactinomyces sp. was isolated and purified by affinity chromatography on bacitracin adsorbents. The enzyme homogeneity was established by SDS electrophoresis (Mr = 38 000) and isoelectrofocusing in PAAG (pI 5.3). Carboxypeptidase T reveals a mixed specificity in comparison with pancreatic carboxypeptidases A and B and cleaves with nearly the same efficiency the peptide bonds formed by the C-terminal residues of basic and neutral hydrophobic amino acids. The enzyme is insensitive to serine and thiol proteinase inhibitors but is completely inhibited by EDTA and o-phenanthroline. The maximal enzyme activity is observed at pH 7-8. With an increase of temperature from 20 to 70 degrees C the enzyme activity is enhanced approximately 10-fold. In the presence of 1 mM Ca2+ the enzyme thermostability is also increased. In terms of some properties, e.g. substrate specificity carboxypeptidase T is similar to metallocarboxypeptidase secreted by Streptomyces griseus. The N-terminal sequence of carboxypeptidase T: Asp-Phe-Pro-Ser-Tyr-Asp-Ser-Gly- Tyr-His-Asn-Tyr-Asn-Glu-Met-Val-Asn-Lys-Ile-Asn-Thr-Val-Ala-Ser-Asn-Tyr- Pro-Asn - Ile-Val-Lys-Thr-Phe-Ser-Ile-Gly-Lys-Val-Tyr-Glu-Gly-Xaa-Gly-Leu- coincides by 21% with that of pancreatic carboxypeptidases A and B. Thus, it may be concluded that these enzymes originate from a common precursor.