Purification and properties of three intracellular proteinases from Candida albicans

Three intracellular proteinases termed A, B and C were purified to homogeneity from the unicellular form of the yeast Candida albicans. Enzyme A is an aspartic proteinase that acts on a variety of proteins. Its optimal pH is around 5 and it is displaced to 6.5 by KSCN. It is not significantly inhibited by PMSF, TLCK (Tos-Lys-CHCl2) or soybean trypsin inhibitor but it is inhibited by pepstatin. Its molecular weight is 60 000. Enzyme B is a dipeptidase that acts on esters or on dipeptides without blocks in either the carboxyl or amino ends. Its pH optimum is around 7.5 and the molecular weight is 57 000. It is inhibited by PMSF, TLCK and DANME (N2Ac-Nle-OMe). Proteinase C is an aminopeptidase with an optimum pH around 8. Its molecular weight was 67 000 when determined by SDS gel electrophoresis and 243 000 when determined by gel weight was 67 000 when determined by SDS gel electrophoresis and 243 000 when determined by gel filtration. It is active towards dipeptides in which at least one amino acid is apolar and is not active when the N-terminal amino acid is blocked. It is inhibited by EDTA or o-phenanthroline and activated by several divalent cations.

LD-carboxypeptidase activity in Escherichia coli. II. Isolation, purification and characterization of the enzyme from E. coli K 12

A LD-carboxypeptidase from Escherichia coli K 12 was isolated by Tris-EDTA treatment and purified to electrophoretic homogeneity by DEAE-cellulose chromatography. The enzyme has a molecular weight of approximately 12,000 as determined by sodium dodecyl sulfate-polyacrylamide electrophoresis and by Sephadex G-100 gel filtration. The studies of the substrate specificity of the enzyme revealed that UDP-MurNAc-tetrapeptide is a superior substrate, with a Km value of 1 X 10(-4) mol/l. The activity of the LD-carboxypeptidase was inhibited by D-amino acids and the beta-lactam antibiotic nocardicin A. Ki values of 0.3 and 43 mmol/l were determined for nocardicin A and D-homoserine, respectively. The properties of the purified enzyme correspond to activity I in ether treated cells.

Improved purification and some properties of bovine lysosomal carboxypeptidase B

Lysosomal carboxypeptidase B (peptidyl-L-amino-acid hydrolase, EC 3.4.18.1) from bovine spleen purified to apparent homogeneity was found to have a molecular weight of 52 000 in the absence and of 25 000 in the presence of urea, determined by gel filtration, indicating the existence of two subunits of identical size. The amount of approx. 15% carbohydrate estimated after cleavage by endoglycosidase H was shown to be insignificant for enzymatic activity. The isoelectric focusing separated lysosomal carboxypeptidase B into several protein bands - each enzymatically active - with a range of isoelectric points between 4.6 and 5.2. The titration of the sulphydryl group in the active site of the enzyme with the proteinase inhibitor E-64 yielded one thiol group per molecule. A maximum of activation was achieved by the addition of selenocystamine together with dithioerythritol and EDTA in the incubation solution. Under these conditions the carboxypeptidase hydrolyzed benzoylglycylarginine (80 kat/mol enzyme), benzoylarginine amide (38 kat/mol enzyme) and carbobenzoxyglutaryltyrosine (110 kat/mol enzyme). Slight enzymatic activities towards benzoylarginine 2-naphthylamide and benzoylarginine p-nitroanilide could be measured. With the oxidized insulin B chain, lysosomal carboxypeptidase B exhibited only carboxypeptidase activity.

Pteroylpolyglutamate hydrolase from human jejunal brush borders. Purification and characterization

Pteroylpolyglutamate hydrolase was solubilized with Triton X-100 from human jejunal mucosal brush borders and purified approximately 5,000-fold using organomercurial affinity chromatography, DEAE-cellulose chromatography, and gel filtration. The apparent molecular weight of the purified enzyme in the Triton micelle was estimated as 700,000 using Bio-Gel A-1.5m gel filtration. Sodium dodecyl sulfate/urea-polyacrylamide gel electrophoresis followed by Coomassie stain demonstrated two polypeptide bands at 145,000 and 115,000 daltons. The purified enzyme had an isoelectric point of 7.2, was maximally active at pH 5.5, and was stable above pH 6.5 and at temperatures up to 65 degrees C for at least 90 min. Human jejunal brush-border pteroylpolyglutamate hydrolase is an exopeptidase which liberated [14C]Glu as the sole labeled product of PteGlu2[14C]Glue (where PteGlun represents pteroylpolyglutamate), failed to liberate a radioactive product from PteGlu2[14C]GluLeu2, and released all possible labeled PteGlun products during incubation with Pte[14C]GluGlu6 with the accumulation of Pte[14C]Glu. PteGlu2, PteGlu3, and PteGlu7 were substrates, each with Km = 0.6 microM, whereas PteGlu was a weak inhibitor of the hydrolysis of PteGlu3 with Ki = 20 microM. Components of the pteroyl moiety, Glu, and short chain Glun in alpha or gamma linkages were not inhibitory. The enzyme was activated by Zn2+ or Co2+. The properties of brush-border pteroylpolyglutamate hydrolase are different from those described for the soluble intracellular pteroylpolyglutamate hydrolase in other species and in human mucosa, yet are consistent with previous data on the process of hydrolysis of PteGlun in the intact human intestine.

Kininase one-an'-a-half: the newest member of the kininase family

A kininase I-like enzyme (carboxypeptidase) was purified to homogeneity from human urine and compared to the 48,000 mol. wt. (48K) active subunit of carboxypeptidase N. The urinary carboxypeptidase had a mol. wt. of 73,000 in gel filtration and 76,000 in SDS-polyacrylamide gel electrophoresis. It had a pH optimum of 7.0 and differed from the 48K subunit in stability, susceptibility to trypsin, and enzymatic activity. The urinary enzyme did not cross-react with antibody to carboxypeptidase N in "Western blotting". Urine from a patient genetically deficient in plasma carboxypeptidase N (21% of normal) contained normal levels of urinary carboxypeptidase with similar properties to that from pooled human urine. Membrane fractions from several tissues contained a similar carboxypeptidase activity. The activity was highest in a microvillous membrane fraction from human placenta (65 nmol/min/mg with Bz-Gly-Lys as substrate). High specific activities were also found in membrane fractions of human kidney (18 nmol/min/mg) and lung (8 nmol/min/mg). The membrane-bound enzyme was distinguished from lysosomal and catheptic carboxypeptidases as well as "enkephalin convertase" by the use of specific inhibitors. These results show that urine contains a carboxypeptidase capable of cleaving arginine or lysine from the C-terminus of peptides. The enzyme does not arise from plasma carboxypeptidase N, but may be released into the urine from the renal brush border.

Existence of ternary complexes of procarboxypeptidase A in the pancreas of some ruminant species

The existence of procarboxypeptidase A, in the form of a non-covalent ternary complex containing the apparently inactive serine protease (subunit III), has so far been observed only in the ox pancreas. Evidence, obtained in the present study, shows that a ternary complex of procarboxypeptidase A, with a subunit III highly homologous with that of the bovine complex, is also present in two other ruminant species, sheep and goat. The biological significance of these complex forms of procarboxypeptidase A and the consistently high biosynthesis level of the apparently inactive subunit III in all three ruminant species is still unknown. Yet the synthesis of subunit III is not related to the animal diet since in the horse, which is a non-ruminant herbivorous animal, the procarboxypeptidase A is monomeric. Reassociation assays between either bovine subunits II or III and monomeric as well as binary forms of procarboxypeptidase A from various species show that, unlike subunit II, the recognition site for subunit III is highly conserved in all the procarboxypeptidases A and that bovine subunit II is different from porcine chymotrypsinogen C with regard to association.

Separation of enkephalin-degrading enzymes from longitudinal muscle layer of bovine small intestine. Enzyme inhibition by arphamenine A

The enkephalin-degrading enzymes, such as aminopeptidase, dipeptidyl aminopeptidase, dipeptidyl carboxypeptidase and carboxypeptidase, were purified partially by DEAE-cellulose column chromatography, using longitudinal muscle from bovine small intestine. These enzyme were inhibited by EDTA and o-phenanthroline. Several protease inhibitors of microbial origin, and synthetic compounds, were tested for their abilities to inhibit these enkephalin-degrading enzymes. Among them, arphamenine A, a new potent inhibitor for aminopeptidase B, was shown to be a useful compound in inhibiting all of the enkephalin-degrading enzymes in small intestine.

Preparative isolation of the two forms of pig pancreatic pro-(carboxypeptidase A) and their monomeric carboxypeptidases A

A method is reported for the preparative isolation of the two forms of pro-(carboxypeptidase A) from pig pancreas: the monomer and the binary complex with pro-(proteinase E). This method, which is mainly based on chromatography on DEAE-Sepharose at pH 5.7, allows these proenzymes to be prepared more quickly and in safer conditions than with other reported methods. Undegraded and homogeneous carboxypeptidase A1 and A2 species (peptidyl-L-amino acid hydrolase, EC 3.4.17.1), in monomeric forms with high specific activity, are also obtained in high yield by controlled trypsin activation of either of the pro-(carboxypeptidases A) followed by chromatography on DEAE-Sepharose at pH 5.8 under dissociating conditions (7 M-urea).

Proteins of the kidney microvillar membrane. Purification and properties of carboxypeptidase P from pig kidneys

Carboxypeptidase P has been purified by immunoaffinity chromatography from pig kidneys. A single-step assay with Z-Pro-Met (where Z represents benzyloxycarbonyl) as substrate was used, methionine being determined by using L-amino acid oxidase and horseradish peroxidase. The enzyme constitutes about 1.5% of the kidney microvillar proteins. Triton X-100-solubilized and papain-released forms of the enzyme were isolated. The former had an apparent subunit Mr of 135 000, and the latter form contained two polypeptide chains of Mr 128 000 and 95 000. The undenatured forms were dimeric proteins. In common with other microvillar hydrolases, carboxypeptidase P was a glycoprotein and each subunit contained one Zn atom. MnCl2 (1 mM) in the assay was necessary for maximum activity; in its absence, 0.5 mM-ZnSO4 produced a limited activation, but was inhibitory at higher concentrations. The Km for Z-Pro-Met, in the presence of MnCl2, was 4.1 mM, and the kcat. for freshly prepared enzyme was 1230 min-1. The enzyme lost activity during storage at -20 degrees C. In a limited survey of peptides, hydrolysis was observed only with substrates containing a proline, alanine or glycine residue in the P1 position, and these included angiotensins II and III. The best substrate in this series was Val-Ala-Ala-Phe.

Human placental neuraminidase. Activation, stabilization and association with beta-galactosidase and its protective protein

Supernatant of homogenized human placenta hardly contains lysosomal neuraminidase activity. It is, however, possible to generate remarkably high activity by concentration of a partially purified glycoprotein fraction. This activity is labile to dilution, but can be stabilized by incubation at 37 degrees C and acid pH. Using beta-galactosidase specific affinity chromatography and immunotitration, we show that the activated and stabilized human lysosomal neuraminidase exists in a complex with beta-galactosidase. Sucrose density gradient centrifugation experiments demonstrate that the neuraminidase activity is exclusively present in a high density multimeric form of beta-galactosidase. The formation of multimeric forms of beta-galactosidase is known to require a 32000-Mr 'protective' protein. Monospecific antibodies against this 'protective' protein were purified from a conventional antiserum containing a mixture of antibodies against the 64000-Mr beta-galactosidase protein and against the 32000-Mr 'protective' protein, using a nitrocellulose blot immunoaffinity purification procedure. Immunotitration experiments with these antibodies show that the 32000-Mr 'protective' protein is present both in association with the beta-galactosidase multimer and with the high-density multimeric form together with neuraminidase. Our data further suggest that association of the 32000-Mr 'protective' protein and another yet unidentified subunit is essential for the catalytic activity of lysosomal neuraminidase. These results explain the absence of neuraminidase activity in the autosomal recessive human lysosomal storage disorder galactosialidosis, where the 32000-Mr 'protective' protein is known to be absent.

Purification and sequencing of the active site tryptic peptide from penicillin-binding protein 5 from the dacA mutant strain of Escherichia coli (TMRL 1222)

The localization of the active site of penicillin-binding protein 5 from the dacA mutant of Escherichia coli strain TMRL 1222 has been determined. The protein was purified to homogeneity and labeled with [14C] penicillin G. The labeled protein was digested with trypsin, and the active site tryptic peptide was purified by a combination of gel filtration and high-pressure liquid chromatography. Sequencing of the purified [14C]penicilloyl peptide yielded the sequence Arg-Asp-Pro-Ala-Ser-Leu-Thr-Lys, which corresponds to residues 40-47 of the gene sequence (Broome-Smith, J., Edelman, A., and Spratt, B. G. (1983) in The Target of Penicillin (Hakenbeck, R., Holtje, J.-V., and Labischinski, H., eds) pp. 403-408, Walter de Gruyter, Berlin). The catalytic amino acid residue that forms a covalent bond with penicillin was identified by treating the purified [14C]penicilloyl peptide with a mixture of proteases and then separating the radioactive products using high-pressure liquid chromatography. Analysis of the radioactive peaks by amino acid analysis confirmed that it is the serine residue that reacts with the beta-lactam ring of penicillin.

Purification and properties of carboxypeptidase G2 from Pseudomonas sp. strain RS-16. Use of a novel triazine dye affinity method

A folate-degrading enzyme, carboxypeptidase G2, has been purified on a large scale from Pseudomonas sp. strain RS-16. Homogeneous enzyme was obtained by a three-step procedure involving ion-exchange chromatography and a novel triazine dye (affinity) chromatography step which utilizes Zn2+ to promote adsorption of the enzyme. Enzyme was selectively eluted by the use of a chelating agent (EDTA) and a step change in pH. The enzyme is a dimeric protein (Mr 83000) with two identical subunits of 41800 and contains four atoms of zinc per enzyme molecule, which are required for full activity. The enzyme follows Michaelis-Menten kinetics with Km values of 4.0 microM for folate, 8.0 microM for methotrexate and 34.0 microM for 5-methyltetrahydrofolate, the predominant form of reduced folate found in plasma.

Properties of kininase in rat dental pulp

A kininase, capable of degrading bradykinin, was partially purified from the dental pulp of rats, and its properties were investigated. Chromatography on both Sephadex G-200 and DEAE Sephadex A-50 columns gave a single peak of kininase activity. The molecular weight of the enzyme, estimated by gel filtration, was about 67,000, and the optimum pH for the enzymatic reaction was about 7.5. The enzyme appears to contain a labile SH group(s) that is essential for its activity, because CdCl2, HgCl2 (0.1 mM each), and p-chloromercuric benzoate (0.05 mM) inhibited the enzyme completely, while dithiothreitol retarded the loss of activity during storage. Of various peptides tested, bradykinin was the substrate most sensitive for the enzyme. The enzyme released several amino acids located in the C-terminal regions of bradykinin--angiotensin I and neurotensin--but only one C-terminal amino acid from des-Arg9--bradykinin and angiotensin II. In contrast, the enzyme did not release any amino acids from substance P, of which only the two amino acids in the N-terminal region are the same as those of bradykinin, but its C-terminal is blocked by an amino group. Although the enzyme was not so highly purified as to rule out the contribution of other peptidases, these results suggest that the dental pulp of rats may contain a single enzyme that degrades bradykinin, and the enzyme may be a type of carboxypeptidase, differing from known kininases from other animal sources.

Purification of a human urinary carboxypeptidase (kininase) distinct from carboxypeptidases A, B, or N

A carboxypeptidase which cleaves basic C-terminal amino acids from peptides was purified from concentrated human urine by a three-step procedure: chromatography on Affi-Gel Blue, arginine-Sepharose affinity chromatography, and gel filtration by HPLC on a TSK-G3000SW column. Urinary carboxypeptidase was purified 406-fold with an 11% yield and a specific activity of 49 mumol/min/mg with benzoylglycylargininic acid as substrate. It migrated as a single band of Mr 75,700 in polyacrylamide gel electrophoresis with sodium dodecyl sulfate. It cleaved benzoylglycylarginine, benzoylglycyllysine, benzoylglycylargininic acid, benzoylalanyllysine, and benzoylphenylalanyllysine at different relative rates than human plasma carboxypeptidase N, the Mr 48,000 active subunit of carboxypeptidase N or human pancreatic carboxypeptidase B. Urinary carboxypeptidase did not hydrolyze benzoylglycylphenylalanine, a substrate of carboxypeptidase A, but readily cleaved bradykinin with a Km of 46 microM and a Kcat of 32 min-1. Its activity was enhanced by CoCl2 and inhibited by cadmium acetate, o-phenanthroline, or DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid. The enzyme had a pH optimum of 7.0 and its activity dropped at pH 6.0 by 60%. It was stable for at least 2 h at 37 degrees C (pH 8.0) but was unstable at room temperature below pH 4.5. The molecular weight, electrophoretic mobility, and activity of urinary carboxypeptidase was not affected by trypsin. The effect of pH and stability further distinguished the urinary carboxypeptidase from other human carboxypeptidases. Urinary carboxypeptidase was immunologically distinct from carboxypeptidase N when analyzed by the "Western blot" technique. Thus, human urine contains a basic carboxypeptidase, different from known carboxypeptidases, which may be released into the urine by the kidney. Here it could inactivate kinins and other peptides containing a basic C-terminal amino acid.

Enzymes in placental microvilli: angiotensin I converting enzyme, angiotensinase A, carboxypeptidase, and neutral endopeptidase ("enkephalinase")

Microvilli from human placental syncytiotrophoblast are rich in angiotensin I converting enzyme (ACE), aminopeptidase A, a carboxypeptidase N-like enzyme, and a neutral endopeptidase (NEP). The specific activities of these enzymes were enhanced in microvillus-enriched fractions obtained by differential centrifugation: Purified microvilli were isolated in a discontinuous sucrose gradient. The placental microvilli hydrolyzed angiotensin II, vasopressin and oxytocin as shown by high pressure liquid chromatography. The inhibitors, bestatin, phosphoramidon, and o-phenanthroline, established the specificity of the enzymes. Aminopeptidase A (angiotensinase A) cleaved angiotensin II to angiotensin III and Asp1. NEP from placenta and from human kidney hydrolyzed oxytocin at the Pro7-Leu8 bond to yield oxytocin 1-7 and leucyl-glycine amide, but did not hydrolyze vasopressin. Vasopressin was cleaved by aminopeptidases in the placental membranes. On electroblotting placental NEP appeared as a double band with a molecular weight slightly higher than the 90,000 of the purified kidney enzyme. Neuraminidase treatment reduced the molecular weight of the placental enzyme to approximately 90,000, indicating that it contains a large amount of sialic acid. The microvilli of human placenta are thus rich in enzymes that may regulate passage of peptides at the maternal-fetal interface.

Two-step dissociation of bovine 6S procarboxypeptidase A by dimethylmaleylation

Reversible condensation of the ternary complex form of bovine pancreatic procarboxypeptidase A with 2,3-dimethyl maleic anhydride was investigated at pH 9.0 and low concentration of reagent over the acylable amino groups. After subsequent modification of only a few lysyl residues, subunit III was found to have been released from the quaternary structure leading to the separation of an apparently native protein devoid of any contaminating subunit II, while dissociation of the remaining binary complex occurred upon further addition of the anhydride. This observation suggests that the electrostatic interactions existing between subunits I and III are more rapidly weakened than those between subunits I and II, probably because fewer lysyl residues are involved and/or there is greater accessibility to the chemical reagent . Although completely inactive on the specific substrates of trypsin, chymotrypsin and elastase, subunit III hydrolyzed p-nitrophenyl acetate at a rate similar to that of chymotrypsin but without any burst of p-nitrophenol, which indicates that the weakly functional active site of the subunit is not quite comparable to that of serine protease zymogens. Subunit III already has some of the functional characteristics of the corresponding active enzymes.

Isolation and characterization of pteroylpolyglutamate hydrolase from rat intestinal mucosa

Pteroylpolyglutamate hydrolase was isolated from rat intestinal mucosa and purified with the aid of affinity chromatography. The affinity ligand was poly-gamma-glutamic acid (Mr approximately 12,000) derived from Bacillus subtilis. The specific enzymatic activity was increased 2,000-fold over the 100,000 X g supernatant of the mucosal homogenate with a yield of 20%. Sephadex G-200 gel filtration yielded an estimated molecular mass of 80,000 daltons. The isoelectric point was pH 8.2. The pH optimum in acetate buffer containing 1 mM zinc was 4.5. The KM values for pteroylheptaglutamate and pteroyltriglutamate were 0.21 and 0.67 microM, respectively. Polyanionic compounds, poly-gamma-glutamic acid, dextran sulfate, and heparin were noncompetitive inhibitors. Studies of the time course of hydrolysis of synthetic [3H]pteroylheptaglutamate by three separate techniques demonstrated the appearance of [3H]pteroylmonoglutamate, synchronous with substrate cleavage. Intermediate pteroyloligoglutamates were not detected. An endopeptidase-like mode of hydrolysis was further established by identification of a hexaglutamyl peptide as the other reaction product.

Peptidyl-D-amino acid hydrolase from Loligo vulgaris Lam. Purification and characterization

An enzyme, tentatively called peptidyl-D-amino acid hydrolase, has been purified from digestive juice from cecum intestine of Loligo vulgaris. The enzyme hydrolyzes peptides that have a low number of D- or L-amino acids. Proteins, polypeptides, and amino acid derivatives are not hydrolyzed. The enzyme acts as a carboxypeptidase with specificity toward small peptides. Polyacrylamide gel electrophoresis, polyacrylamide gel isoelectric focusing, and gel filtration showed the enzyme to be homogeneous. The native enzyme has Mr = 140,000 and consists of two subunits of Mr = 106,000 and 36,000, respectively. The enzyme has an isoelectric point at pH 6.1. The extinction coefficient is 336,000 at 278 nm and the absorption spectrum reveals no chromophoric cofactors. The apparent Km values for Gly-D-Ala, Gly-L-Ala, L-Ala-D-Ala, L-Ala-L-Ala, D-Leu-D-Leu, and L-Leu-L-Leu are 5.2, 7.7, 2.5, 2.8, 5.4, and 8.6 mM, respectively. The enzyme also hydrolyzes Leu-enkephalin, Met-enkephalin, and [D-Ala2] X Met-enkephalin. It has a broad pH optimum from 7.2 to 8.8 with a maximum at pH 8.0. The enzyme activity is not inhibited or increased by Co2+, Mn2+, Mg2+, Zn2+, Cu2+, and Ca2+ at a concentration of 1 mM or by guanidine chloride (50 mM)urea (3 M), and EDTA (50 mM). 50 mM CaCl2, 1 mM CdCl2, and 1 mM Pb(CH3COO)2 inhibited the enzyme activity by 5-10%. Amino acid analysis of the purified enzyme revealed an abundance of aspartic acid, glutamic acid, glycine, and valine. We hypothesize that the enzyme described here serves to hydrolyze D-amino acid peptides, which are probably present in the nervous system of cephalopods.

Purification and characterization of a membrane-bound enkephalin-forming carboxypeptidase, "enkephalin convertase"

Enkephalin convertase, the enkephalin-synthesizing carboxypeptidase B-like enzyme, has been purified to apparent homogeneity from bovine pituitary and adrenal chromaffin granule membranes. The membrane-bound enkephalin convertase can be solubilized in high yield with 0.5% Triton X-100 in the presence of 1 M NaCl. Extensive purification is achieved by affinity chromatography with p-aminobenzoyl-L-arginine linked to Sepharose 6B. Enzyme purified from both pituitary and adrenal chromaffin granule membranes shows a single band by sodium dodecyl sulfate polyacrylamide gel electrophoresis with an apparent molecular weight of 52,500, whereas enkephalin convertase purified from soluble extracts of these tissues has an apparent molecular weight of 50,000. The regional distribution of the membrane-bound enzyme in the rat brain differs from that of the soluble enzyme. While the soluble enzyme shows 10-fold variations, resembling somewhat the enkephalin peptides, membrane-bound enkephalin convertase is more homogeneously distributed throughout the brain. In rat pituitary glands, membrane-bound enzyme activity is similar in the anterior and posterior lobes, whereas the soluble enzyme is enriched in the anterior lobe. Membrane-bound and soluble forms of enkephalin convertase isolated from either bovine pituitary glands or adrenal chromaffin granules show identical substrate and inhibitor specificities. As with the soluble enzyme, membrane-bound enkephalin convertase hydrolyzes [Met]- and [Leu]enkephalin-Arg6 and -Lys6 to enkephalin, with no further degradation of the pentapeptide.

[Carboxypeptidase T--intracellular carboxypeptidase of Thermoactinomycetes--a distant analog of animal carboxypeptidase]

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.