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PubMed1985

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).

Animals↗

PubMed1995

Purification and characterization of carboxypeptidase D, a novel carboxypeptidase E-like enzyme, from bovine pituitary.

Carboxypeptidase E (CPE) is involved in the biosynthesis of most neuropeptides and peptide hormones. Until recently, CPE was the only intracellular carboxypeptidase thought to be involved in neuroendocrine peptide processing. However, the finding that fat/fat mice, which have a mutation within the CPE gene that inactivates the enzyme, are capable of a reduced amount of insulin processing suggests that another carboxypeptidase is present within the secretory pathway. We have detected a CPE-like enzyme, designated CPD, which has many properties in common with those of CPE. Like CPE, CPD is a metallocarboxypeptidase that has a pH optimum of 5.5-6. The Km and Kcat values for a series of short peptide substrates show only minor differences between CPD and CPE. Several active site-directed inhibitors also show generally similar potency toward the two enzymes, although guanidinoethylmercaptosuccinic acid is approximately 10-fold more potent, and hippuryl-Arg is approximately 100-fold more potent as an inhibitor of CPD than of CPE. A major difference between the two enzymes is the molecular masses; CPE is 50,000-56,000, whereas CPD is approximately 180,000. Also, CPD does not elute from a substrate affinity column when the pH is raised to 8, which elutes CPE, although CPD can subsequently be eluted by arginine. Both CPE and CPD are present in purified bovine anterior pituitary secretory vesicles, but the tissue distribution of CPD is more uniform than that of CPE. Antisera to the N- and C-terminal regions of CPE do not recognize CPD. The partial N-terminal amino acid sequence of bovine CPD shows 30-40% homology with an N-terminal region of bovine and rat CPE and 70% homology with a duck protein known as gp180, a hepatitis B virus particle binding protein that shows 47% homology to CPE. Taken together, these results suggest that CPD is a novel secretory pathway enzyme that may be the bovine homologue of gp180.

Amino Acid Sequence↗

PubMed1988

Structural characterization of the rat carboxypeptidase A1 and B genes. Comparative analysis of the rat carboxypeptidase gene family.

Nucleotide sequencing of a rat carboxypeptidase B (CPB) cDNA and direct sequencing of the CPB mRNA via primer extension on pancreatic polyadenylated RNA has yielded the complete amino acid sequence of rat CPB. The rat enzyme is synthesized as a precursor species containing a large amino-terminal fragment (108 amino acids) that contributes a putative signal sequence and an activation peptide. The mature form of rat CPB is homologous to bovine CPB (77% identity); the amino acids in bovine CPB which have been previously implicated in catalysis or ligand binding are invariant in the rat orthologue. The rat CPB cDNA was used as a probe for the isolation of the rat CPB gene. Detailed characterization of three overlapping rat genomic clones demonstrated that the coding region for the rat CPB precursor is sequestered in 11 exons which are dispersed throughout 34 kilobase pairs of genomic DNA. The nucleotide sequence of a large part of the gene has been determined including that of the exons, the exon/intron boundaries, and the 5' flanking region. We also report the partial nucleotide sequence of the rat CPA1 gene. Comparative analysis of the structural organization of the rat CPB, rat CPA1, and rat CPA2 genes (Gardell, S. J., Craik, C. S., Clauser, E., Goldsmith, E. J., Stewart, C.-B., Graf, M., and Rutter, W. J. (1988) J. Biol. Chem. 263, 17828-17836) reveals that, with one exception, the number, position, and sequence composition of the exons in these three carboxypeptidase genes are conserved in spite of considerable divergence with respect to the lengths of their corresponding intervening sequences. Conserved sequences in the 5' flanking regions of the rat CPA1, CPA2, CPB, and other pancreas-specific genes have been identified.

Amino Acid Sequence↗

PubMed1989

An arginine specific carboxypeptidase generated in blood during coagulation or inflammation which is unrelated to carboxypeptidase N or its subunits.

An unstable carboxypeptidase N or B like enzyme is generated as a result of coagulation. This enzyme is derived from some plasma component (s) and not from blood cells or platelets. Furthermore, the activity generated is specific for arginine substrates insofar as small synthetic substrates are concerned. The enzyme is unrelated to CPN or any of its subunits or subunit fragments. This transient carboxypeptidase may be involved in the processing and/or scheduling of different functions of bioactive peptides generated during inflammation.

Arginine↗

PubMed1999

Catalytic activity of carboxypeptidase B and of carboxypeptidase Y with anisylazoformyl substrates.

Anisylazoformyllysine (CH3OC6H4-N = N-CO-Lys-OH) is rapidly hydrolyzed at the acyl-lysine linkage by the zinc-enzyme porcine carboxypeptidase B. The catalytic reaction is readily monitored spectrophotometrically by disappearance of the intense absorption (348.5 nm, epsilon 18400) of the azo chromophore, which chemically fragments after substrate cleavage. Carboxypeptidase Y has no activity toward this type of substrate.

Animals↗

PubMed2000

Contribution of C-tail residues of potato carboxypeptidase inhibitor to the binding to carboxypeptidase A A mutagenesis analysis.

The role of each residue of the potato carboxypeptidase inhibitor (PCI) C-terminal tail, in the interaction with carboxypeptidase A (CPA), has been studied by the analysis of two main kinds of site-directed mutants: the point substitution of each C-terminal residue by glycine and the sequential deletions of the C-terminal residues. The mutant PCI-CPA interactions have been characterized by the measurement of their inhibition constant, Ki, in several cases, by their kinetic association and dissociation constants determined by presteady-state analysis, and by computational approaches. The role of Pro36 appears to be mainly the restriction of the mobility of the PCI C-tail. In addition, and unexpectedly, both Gly35 and Pro36 have been found to be important for folding of the protein core. Val38 has the greatest enthalpic contribution to the PCI-CPA interaction. Although Tyr37 has a minor contribution to the binding energy of the whole inhibitor, it has been found to be essential for the interaction with the enzyme following the cleavage of the C-terminal Gly39 by CPA. The energetic contribution of the PCI secondary binding site has been evaluated to be about half of the total free energy of dissociation of the PCI-CPA complex.

Amino Acid Sequence↗

PubMed1986

LD-carboxypeptidase activity in Escherichia coli. I. The LD-carboxypeptidase activity in ether treated cells.

The activities of the LD-carboxypeptidases of Escherichia coli K 12 and of a mutant strain 155 with reduced activities were studied with the aid of ether treated cells. Evidence was obtained that was consistent with the suggestion that in both strains two LD-carboxypeptidase activities are present. Activity I degrades the nucleotide activated precursor UDP-MurNAc-tetrapeptide and activity II splits off D-alanine residues from position 4 of the peptide subunits in the nascent murein. In the mutant strain activity I is reduced 10fold compared with strain K 12, whereas activity II is not affected. The two activities could be distinguished with regard to their sensitivity to D-amino acids and the beta-lactam antibiotic thienamycin.

Alanine↗

PubMed1986

The potential of carboxypeptidase G2-antibody conjugates as anti-tumour agents. I. Preparation of antihuman chorionic gonadotrophin-carboxypeptidase G2 and cytotoxicity of the conjugate against JAR choriocarcinoma cells in vitro.

Carboxypeptidase G2, a zinc metalloenzyme isolated from Pseudomonas sp. strain RS-16, which catalyses the hydrolytic cleavage of reduced and non-reduced folates to pteroates and L-glutamate, has been linked to a monoclonal antibody (W14A) raised to human chorionic gonadotrophin. The coupling efficiency and retention of antibody and enzymatic activities are compared for three separate methods of preparing 1:1 conjugates. Preliminary in vitro studies on the cytotoxicity of the free enzyme and the conjugated enzyme towards JAR choriocarcinoma cells are reported. Despite the limitations of the in vitro model, it could be demonstrated that a significant proportion of 10(6) choriocarcinoma cells lost viability when exposed to either free or conjugated enzyme for 72 hours at concentrations of carboxypeptidase G2 of 1-3 units ml-1 of medium.

Antibodies, Monoclonal↗

PubMed1971

New forms of bovine carboxypeptidase B and their homologous relationships to carboxypeptidase A.

Two new forms of carboxypeptidase B have been isolated from spontaneously activated bovine pancreatic juice. The fully active enzymes contain an internal split at residues 92-93 and 95-96, respectively. Sequenator analysis of the amino terminal segments of the two chains of the enzyme has extended the sequence information by 51 amino acid residues. Comparison of 125 residues strengthens the hypothesis that carboxypeptidases A and B are homologous both in amino acid sequence and in three-dimensional conformation and implicates Asp-255 as the anionic site of substrate binding of the B enzyme.

Amino Acid Sequence↗

PubMed1998

Aortic carboxypeptidase-like protein, a novel protein with discoidin and carboxypeptidase-like domains, is up-regulated during vascular smooth muscle cell differentiation.

Phenotypic modulation of vascular smooth muscle cells plays an important role in the pathogenesis of arteriosclerosis. In a screen of proteins expressed in human aortic smooth muscle cells, we identified a novel gene product designated aortic carboxypeptidase-like protein (ACLP). The approximately 4-kilobase human cDNA and its mouse homologue encode 1158 and 1128 amino acid proteins, respectively, that are 85% identical. ACLP is a nonnuclear protein that contains a signal peptide, a lysine- and proline-rich 11-amino acid repeating motif, a discoidin-like domain, and a C-terminal domain with 39% identity to carboxypeptidase E. By Western blot analysis and in situ hybridization, we detected abundant ACLP expression in the adult aorta. ACLP was expressed predominantly in the smooth muscle cells of the adult mouse aorta but not in the adventitia or in several other tissues. In cultured mouse aortic smooth muscle cells, ACLP mRNA and protein were up-regulated 2-3-fold after serum starvation. Using a recently developed neural crest cell to smooth muscle cell in vitro differentiation system, we found that ACLP mRNA and protein were not expressed in neural crest cells but were up-regulated dramatically with the differentiation of these cells. These results indicate that ACLP may play a role in differentiated vascular smooth muscle cells.

Adult↗

PubMed1992

Purification and characterization of a thermostable carboxypeptidase (carboxypeptidase Taq) from Thermus aquaticus YT-1.

A thermostable carboxypeptidase, which we named carboxypeptidase Taq, was purified from Thermus aquaticus YT-1 and characterized. The molecular weight of the enzyme was estimated to be about 56,000 and 58,000 on SDS-polyacrylamide gel electrophoresis and gel filtration, respectively, indicating that the enzyme has a monomeric structure. The optimum pH of the enzyme was 8.0, and the optimum temperature for the reaction was 80 degrees C. The enzyme activity was dependent on cobalt ion and was inhibited by metal-chelating reagents, indicating that the enzyme is a metalloenzyme. The enzyme had high thermostability independent of cobalt ion; about 90% of its activity remained even after treatment at 80 degrees C for 5 h. The enzyme showed broad substrate specificity, although proline at the C-terminus of peptides was not cleaved. The enzyme released amino acids sequentially from the C-terminus.

Amino Acid Sequence↗

PubMed1978

Stability of D-5,5-dimethyl-delta2-thiazoline-4-carboxylic acid in relation to its possible occurrence as a degradation product of penicillin by the exocellular DD-carboxypeptidase-transpeptidase from Streptomyces R61 and the membrane-bound dd-carboxypeptidase from Bacillus stearothermophilus.

The stability of D-5,5-dimethyl-delta2-thiazoline-4-carboxylic acid has been studied under various conditions. In 10 mM cacodylate, pH 6.5, and at 55 degrees C, D-5,5-dimethyl-delta2-thiazoline-4-carboxylic acid (at concentrations lower than 1 mM) is hydrolyzed into N-formyl-D-penicillamine with a half-life of 3 to 4 min. On this basis, it is very unlikely that D-5,5-dimethyl-delta2-thiazoline-4-carboxylic acid could be one of the end products resulting from the cleavage of benzylpenicillin by the DD-carboxypeptidase of Bacillus stearothermophilus (as reported by Hammarström and Strominger (1976) J. Biol. Chem. 251, 7947--7949). In 3 mM phosphate, pH 7.5, and at 37 degrees C, D-5,5-dimethyl-delta2-thiazoline-4-carboxylic acid (at concentrations lower than 1 mM) has a half-life of 45 min. On the basis of kinetic experiments carried out under these conditions with phenoxymethylpenicillin and the DD-carboxypeptidase-transpeptidase of Streptomyces R61, it is concluded that the primary product which arises from the thiazolidine moiety of the antibiotic molecule and gives rise to N-formyl-D-penicillamine, has a half-life of 10 min, a value which is not compatible with the hypothesis that D-5,5-dimethyl-delta2-thiazoline-4-carboxylic acid would be an intermediate involved in the fragmentation pathway.

Acyltransferases↗

PubMedDate not supplied

[Tissue and regional distribution of activity of phenylmethylsulfonyl fluoride inhibited carboxypeptidase and other carboxypeptidases in rats].

Phenylmethylsulfonyl fluoride (PMSF)-inhibited carboxypeptidase (CP) is recently described exopeptidase, that cleaved arginine residues from C-terminal of enkephalin synthetic analogs. The highest enzyme activity was found in the adrenal gland and 40% lower one was revealed in the pituitary gland. A 2.5-fold lower than PMSF-inhibited CP activity in adrenal glands was present in testes. The enzyme activity in the brain regions, liver and spleen was about 2.3-fold lower than in the pituitary gland. Its activity in kidneys is insignificant. In the brain region the lowest PMSF-inhibited CP activity was observed in hippocamp and optic and auditory hills, the highest enzyme activity, in the olfactory bulbus and cerebral hemispheres. The differences between brain regions with the highest and the lowest PMSF-inhibited CP activity do not exceed 1.5 fold. The tissue and regional distribution of PMSF-inhibited CP correlated with that for CPH, enzyme of regulatory peptides processing, and it did not correlate with the distribution of lysosomal CPB. The results allow one to suggest the involvement of PMSF-inhibited CP in the processing of the precursors of biological active peptides and secretory proteins. The differences of distribution of PMSF-inhibited CP and CPH are probably connected with involvements of these enzymes in the processing of precursors of different regulatory peptides.

Adrenal Glands↗

PubMed1996

A novel [125I]iodinated carboxypeptidase A substrate detects a metallopeptidase activity distinct from carboxypeptidase A in brain.

We have designed two radioactive substrates, hippuryl-L-[3H]phenylalanine and 3-(p-hydroxy, m-[125I]phenyl)propionic acid ([125I]Bolton reagent) derivative of L-arginyl-L-phenylalanine, i.e. [125I]BRF, for a highly sensitive assay of carboxypeptidase A (CPA) activity. After cleavage of the C-terminal phenylalanine residue by CPA, the radioactive product of the reaction was conveniently separated by polystyrene bead chromatography. Using [125I]BRF, typical CPA activity inhibited by 1 microM 2-benzyl-3-mercaptopropanoic acid was detected in extracts from rat pancreas or intestine. In brain and some other tissues, however, [125I]BRF-hydrolyzing activity was only inhibited by this compound in 1000-fold higher concentration, suggesting the participation of a metallopeptidase distinct from CPA.

Animals↗

PubMed2002

Insight into the stereochemistry in the inhibition of carboxypeptidase A with N-(hydroxyaminocarbonyl)phenylalanine: binding modes of an enantiomeric pair of the inhibitor to carboxypeptidase A.

Both D- and L-isomers of N-(hydroxyaminocarbonyl)phenylalanine () were shown to have strong binding affinity towards carboxypeptidase A (CPA) with D- being more potent than its enantiomer by 3-fold (Chung, S. J.; Kim, D. H. Bioorg. Med. Chem. 2001, 9, 185.). In order to understand the reversed stereochemical preference shown in the CPA inhibition, we have solved the crystal structures of CPA complexed with each enantiometer of up to 1.75 A resolution. Inhibitor L- whose stereochemistry belongs to the stereochemical series of substrate binds CPA like substrate does with its carbonyl oxygen coordinating to the active site zinc ion. Its hydroxyl is engaged in hydrogen bonding with the carboxylate of Glu-270. On the other hand, in binding of D- to CPA, its terminal hydroxyl group is involved in interactions with the active site zinc ion and the carboxylate of Glu-270. In both CPA small middle dot complexes, the phenyl ring in is fitted in the substrate recognition pocket at the S(1)' subsite, and the carboxylate of the inhibitors forms bifurcated hydrogen bonds with the guanidinium moiety of Arg-145 and a hydrogen bond with the guanidinium of Arg-127. In the complex of CPA small middle dotD-, the carboxylate of the inhibitor is engaged in hydrogen bonding with the phenolic hydroxyl of the down-positioned Tyr-248. While the L- binding induces a concerted movement of the backbone amino acid residues at the active site, only the downward movement of Tyr-248 was noted when D- binds to CPA.

Binding Sites↗

PubMed2001

Mechanistic insight into the inactivation of carboxypeptidase A by alpha-benzyl-2-oxo-1,3-oxazolidine-4-acetic acid, a novel type of irreversible inhibitor for carboxypeptidase A with no stereospecificity.

On the basis of the active site topology and enzymic catalytic mechanism of carboxypeptidase A (CPA), a prototypical zinc-containing proteolytic enzyme, alpha-benzyl-2-oxo-1,3-oxazolidine-4-acetic acid (1), was designed as a novel type of mechanism-based inactivator of the enzyme. All four possible stereoisomers of the inhibitor were synthesized in an enantiomerically pure form starting with optically active aspartic acid, and their CPA inhibitory activities were evaluated to find that surprisingly all of the four stereoisomers inhibit CPA in a time dependent manner. The inhibited enzyme did not regain its enzymic activity upon dialysis. The inactivations were prevented by 2-benzylsuccinic acid, a competitive inhibitor that is known to bind the active site of the enzyme. These kinetic results strongly support that the inactivators attach covalently to the enzyme at the active site. The analysis of ESI mass spectral data of the inactivated CPA ascertained the conclusion from the kinetic results. The values of second-order inhibitory rate constants (k(obs)/[I](o)) fall in the range of 1.7-3.6 M(-1) min(-1). The lack of stereospecificity shown in the inactivation led us to propose that the ring cleavage occurs by the nucleophilic attack at the 2-position rather than at the 5-position and the ring opening takes place in an addition-elimination mechanism. The tetrahedral transition state that would be generated in this pathway is thought to be stabilized by the active site zinc ion, which was supported by the PM3 semiemprical calculations. In addition, alpha-benzyl-2-oxo-1,3-oxazolidine-5-acetic acid (18), a structural isomer of 1 was also found to inactivate CPA in an irreversible manner, reinforcing the nucleophilic addition-elimination mechanism. The present study demonstrates that the transition state for the inactivation pathway plays a critical role in determining stereochemistry of the inactivation.

Carboxypeptidases↗

PubMed1998

Inhibition of neurotensin-stimulated mast cell secretion and carboxypeptidase A activity by the peptide inhibitor of carboxypeptidase A and neurotensin-receptor antagonist SR 48692.

BACKGROUND: Neurotensin (NT), a peptide found in brain and several peripheral tissues, is a potent stimulus for mast cell secretion and its actions are blocked by the specific NT receptor antagonist, SR 48692. Subsequent to stimulation, NT is rapidly degraded by mast cell carboxypeptidase A (CPA). In the experiments described here, we tested for the involvement of CPA activity in the activation of mast cell secretion by the peptide, NT. METHODS: Mast cells were isolated from the peritoneal and pleural cavities of rats, purified over metrizamide gradients and incubated at 37 degrees C in Locke solution or Locke containing the appropriate inhibitors. For some experiments, media derived from mast cells stimulated by compound 48/80 were used as a source of mast cell CPA activity. RESULTS: Treatment of mast cells with the highly specific peptide inhibitor of CPA derived from potato (PCI) inhibited histamine release in response to NT and NT8-13 (the biologically active region of NT). This inhibition required some 20 min to develop and was only partially reversed by a 20-min wash period. PCI (10 microM) did not inhibit histamine release in response to NT1-12, bradykinin, compound 48/80, the calcium ionophore, A23187, or anti-IgE serum. PCI also inhibited mast cell CPA activity. SR 48692, a highly selective antagonist of the brain NT receptor and of NT-stimulated mast cell secretion, also inhibited mast cell CPA activity as well as bovine pancreatic CPA activity in a concentration-dependent manner. DISCUSSION: It is suggested that the mast cell binding site for NT and the active site for CPA may share similar characteristics. The results are discussed in terms of NT mechanism of action on the mast cell.

Animals↗

PubMed1995

Isolation and characterization of a microbial Arg/Lys carboxypeptidase, carboxypeptidase F.

Carboxypeptidase F was isolated from a fungal strain F-33 and characterized. The enzyme has the ability to release arginine and lysine from the carboxy terminus of peptides, and showed high specific activity against arginine (140 units mg-1 protein). Optimal temperature and pH for the enzyme reaction were 55 degrees C and pH 8.5, respectively. The enzyme possessed a high thermal stability. Native molecular weight was estimated to be approximately 450,000. Enzymatic activity was inhibited by Co2+, Cd2+, chelating agents and thiol inhibitors.

Amino Acid Sequence↗