Disease relevance of Cpa1

• The cDNA was used as a probe to identify DNA fragments containing carboxypeptidase A sequences in a bacteriophage lambda library of rat genomic DNA [1].
• The tumor-derived activity is dialyzable (cutoff, Mr 3500), stable to trypsin treatment and to heating at 56 degrees, but destroyed by heating to 100 degrees or by treatment with Streptomyces griseus protease or carboxypeptidase A. Ultrafiltration suggests a molecular weight of 300 to 1000 [2].

High impact information on Cpa1

• Site-directed mutagenesis shows that tyrosine 248 of carboxypeptidase A does not play a crucial role in catalysis [3].
• In contrast to the solubilized enzyme, the RMCP I activity within the insoluble granules was completely stable for at least 2 months in suitable buffers at pH 8.0 or pH 7.2, at 4 degrees C. Carboxypeptidase A activity associated with isolated mast cell granules was completely inhibited by 10 mM o-phenanthroline [4].
• An almost complete mRNA sequence has been deduced that predicts a polypeptide having 78% amino acid sequence homology with bovine carboxypeptidase A. The amino acid sequence of the activation and signal peptides of the carboxypeptidase A precursor were inferred from the nucleotide sequence [1].
• Rat carboxypeptidase A cDNA clones have been isolated from a cDNA library prepared from pancreatic mRNA [1].
• Neurons expressing latexin, a carboxypeptidase A inhibitor, are restricted to lateral areas in the cerebral cortex of adult and early postnatal rats [5].

Biological context of Cpa1

• Crystallographic studies suggest that Arg-127 is a key amino acid in the hydrolysis of peptides and esters by carboxypeptidase A. The guanidinium group of Arg-127 is hypothesized to stabilize the oxyanion of the tetrahedral intermediate formed by the attack of water on the scissile carbonyl bond [6].
• Carboxypeptidase A isoforms produced by distinct genes or alternative splicing in brain and other extrapancreatic tissues [7].
• The putative substrate binding site resembles that of carboxypeptidase A, although other structural features bear more similarity to carboxypeptidase B. Mast cell carboxypeptidase retains enzymatic activity toward a peptide substrate (angiotensin I) while bound within the granular matrix of the rat connective tissue mast cells [8].
• Localization of the rat T-cell receptor beta-chain and carboxypeptidase A1 loci to chromosome 4 [9].
• Studies on its substrate specificity and sensitivity to inhibitors indicated that cathepsin B and carboxypeptidase A are responsible for almost all the aldolase-inactivating activity in the lysosomal fraction [10].

Anatomical context of Cpa1

• The activities of carboxypeptidase A, dipeptidase and Na+/K+ ATPase were reduced in the mucosa of the proximal end of the small intestine of cadmium exposed rats [11].
• Localization of carboxypeptidase A to the macromolecular heparin proteoglycan-protein complex in secretory granules of rat serosal mast cells [12].
• Latexin, a carboxypeptidase A inhibitor, is expressed in rat peritoneal mast cells and is associated with granular structures distinct from secretory granules and lysosomes [13].
• Trypsin, chymotrypsin and elastase activities in pancreas were 1.4, 2.8 and 2 times higher in diet III than in diet I whereas carboxypeptidase A level was unchanged [14].
• Our data suggest that a CPA-like enzyme could be added to a repertoire of enzymes present in the rat mesangial cells and adventitia of renal blood vessels [15].

Associations of Cpa1 with chemical compounds

• Changes in carboxypeptidase A, dipeptidase and Na+/K+ ATPase activities in the intestine of rats orally exposed to different doses of cadmium [11].
• Treatment of the enzyme with carboxypeptidase A resulted in the release of approximately 0.5 mol each of valine and leucine per 60,000 g of enzyme [16].
• It thus resembles certain metallopeptidases, including carboxypeptidase A and the angiotensin-converting enzyme [17].
• We have replaced this amino acid in rat carboxypeptidase A1 with lysine (R127K), methionine (R127M), and alanine (R127A), in order to define the role of Arg-127 in carboxypeptidase catalyzed hydrolysis [6].
• Carboxypeptidase A liberates 4 mol of COOH-terminal tyrosine/mol of enzyme, and the number of arginine-containing peptides in a tryptic digest of the enzyme is one-fourth of that arginine residues present in the enzyme [18].

Other interactions of Cpa1

• Glucagon1-21 has been prepared by treating native glucagon with carboxypeptidase A. Purified glucagon1-21 did not contain detectable methionine (less than 0.001 residue/mol) and the activity of the compound did not change after treatment with cyanogen bromide as has been shown with native glucagon [19].
• Only one of the exon/intron junctions of the rat CPE gene is present in a comparable position within the genes for carboxypeptidase-A and -B, both of which are only 17-21% homologous to CPE at the amino acid level [20].
• Enkephalinase, a zinc-containing metallo enzyme, displays homology with other zinc metallo enzymes such as carboxypeptidase A, B and E, suggesting enzymatic similarities in these enzymes [21].
• On the other hand, selective inhibition of granule chymase (leaving carboxypeptidase A active) totally abolished the proteolytic degradation of LDL [22].
• The results are consistent with a model according to which the proteolytic degradation of LDL by mast cell granules results from coordinated action of the two granule-bound enzymes, whereby the chymase first cleaves peptides from the apolipoprotein B of LDL, and thereafter the carboxypeptidase A cleaves amino acids from the peptides formed [22].

Analytical, diagnostic and therapeutic context of Cpa1

• Using an immunologic technique for the detection of zymogen activation, CCK was found to stimulate the conversion of procarboxypeptidase A1 to a 35-kD form having the same net charge and electrophoretic mobility as purified recombinant carboxypeptidase A1 [23].
• Using monoclonal antibodies to CPA, Western blot showed the presence of CPA-like enzyme in the extracts prepared from the mesangial cells or kidney cortex of the rat [15].
• By immunofluorescence, all neoplastic cells stained positively for the six enzymes tested: amylase, lipase, carboxypeptidase A, chymotrypsinogen, trypsinogen, and ribonuclease [24].
• A carboxypeptidase A-like enzyme known as cathepsin A was purified from rat brain by extraction with Triton X-100, followed by chromatography on DEAE-Sephadex A-50 and gel-filtration [25].
• Immunohistochemistry showed that CPA-like enzyme is localized in the mesangial glomerular cells and adventitia of kidney blood vessels, whereas it was absent in the renal tubules [15].

References