Properties Of Carboxypeptidase Research Articles

The insulin-secretory-granule carboxypeptidase H. Purification and demonstration of involvement in proinsulin processing.

A carboxypeptidase B-like enzyme was detected in the soluble fraction of purified insulin secretory granules, and implicated in insulin biosynthesis. To investigate the role of this activity further, we purified the enzyme from rat insulinoma tissue by gel-filtration chromatography and affinity elution from p-aminobenzoyl-arginine. A yield of 42%, with a purification factor of 674 over the homogenate, was achieved. Analysis of the purified carboxypeptidase by SDS/polyacrylamide-gel electrophoresis under either reducing or non-reducing conditions showed it to be a monomeric protein of apparent Mr 55,000. The preparation was also homogeneous by high-performance gel-filtration chromatography. The enzyme bound to concanavalin A, showing it to be a glycoprotein. Amino acid analysis or chemical deglycosylation and SDS/polyacrylamide-gel electrophoresis indicated a protein Mr of 50,000, suggesting a carbohydrate content of approx. 9% by weight. The purified enzyme was able to remove basic amino acids from the C-terminus of proinsulin tryptic peptides to generate insulin, but did not further degrade the mature hormone. It was inhibited by EDTA, 1,10-phenanthroline and guanidinoethylmercaptosuccinic acid, and stimulated 5-fold by CoCl2. The pH optimum of the conversion of diarginyl-insulin into insulin was in the range 5-6, with little activity above pH 6.5. Activity was also expressed towards a dansylated tripeptide substrate (dansyl-phenylalanyl-leucyl-arginine; Km = 17.5 microM), and had a pH optimum of 5.5. These properties are indistinguishable from those of the activity located in secretory granules, and are compatible with the intragranular environment. The insulin-secretory-granule carboxypeptidase shared several properties of carboxypeptidase H from bovine adrenal medulla and pituitary. We propose that the carboxypeptidase that we purified is the pancreatic isoenzyme of carboxypeptidase H (crino carboxypeptidase B; EC 3.4.17.10), and is involved in the biosynthesis of insulin in the pancreatic beta-cell.

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.

Studies on pancreatic enzymes in fish. XIV. Purification and some properties of carboxypeptidase A from the catfish pancreas.

Studies on pancreatic enzymes in fish. XIV. Purification and some properties of carboxypeptidase A from the catfish pancreas.

Some properties of porcine carboxypeptidase N.

Some properties of carboxypeptidase N purified from pig serum have been investigated. The amino acid composition resembles that of human carboxypeptidase N, but differs markedly from that of porcine carboxypeptidase B. The enzyme contains a mass fraction of 0.1 carbohydrates. Both ester and peptide substrates are hydrolyzed at the same site. Peptide substrates are hydrolyzed if lysine or arginine is the C-terminal amino acid, and provided that the penultimate amino acid is not proline. Argininic acid and epsilon-aminocaproic acid are good inhibitors of the enzyme.

Ligand bindings of bovine carboxypeptidase B. II. Affinity chromatography and cooperative ligations.

Affinity chromatography was used to characterize the binding properties of carboxypeptidase B with its ligands. The affinity adsorbents employed included arginine directly attached to agarose beads, arginine attached to the same support through hydrophilic and hydrophobic spacers, and immobilized caproylphenylalanine. The enzyme showed marked retardation on all of the arginine columns but only slight retardation on the phenylalanine column. Several hydrophobic ligands in solution enhanced to some extent the enzyme retardation on columns having arginine directly attached to the solid support, while several amino- and guanidino-alkylcarboxylic acids (lysine and arginine analogs) greatly enhanced the enzyme retardation on the phenylalanine column and somewhat enhanced it on the other columns having hydrophobic spacer arms. These observations confirmed that the enzyme has twobinding sites for the soluble and immobilized ligands and that these two sites exhibit cooperative ligations. Binding constants of the enzyme for various soluble ligands were also calculated from their chromatographic effects and the resulting values were interpreted in terms of the cooperative action of the two bindings sites, i.e., one for the primary binding of basic amino acid analogs (SITE I) and the other for hydrophobic compounds (Site II). In this chromatographic study, however, such cooperation of the two sites was obscure when arginine, acylarginine, or alkylarginine was the ligand directing to Site I.

Some properties of carboxypeptidases in germinating rice seeds and rice leaves.

Germinating rice contained three carboxypeptidases or carboxypeptidase-like enzymes which hydrolyzed CPA (carbobenzoxy-l-phenylalanyl-l-alanine) at different pH ranges. The three CPA hydro lases which acted optimally at pH 4, 5 ~ 5.5, and 7. were tentatively termed CPAase-4, CPAase-5, and CPAase-7 respectively. CPAase-4 was contained in resting seeds and endosperms of germinating seeds. Its activity was maximum in resting seeds and gradually decreased during germination. CPAase-5 was absent in resting seeds, and appeared in endosperms and seedlings in the later stages after germinaion. This enzyme was predominant in mature plant leaves. CPAase-7 was detected in the young shoots and young roots during a limited period of germination. Enzymatic properties of CPAase-5 partially purified from rice leaves were very similar to those of carboxypeptidases in various plants.

Isolation and properties of carboxypeptidase from leaves of wounded tomato plants

A carboxypeptidase was purified to homogeneity from upper, unwounded leaves of tomato plants in which carboxypeptidase activity had been induced to increase over three-fold by severely wounding the lower leaves. The carboxypeptidase was purified by ammonium sulfate precipitation, affinity chromatography, and finally by gel permeation chromatography. Electrophoresis at pH 4.3 and isoelectric focusing showed only a single band. The isoelectric point was 5.2 and the MW 105 000. Tomato carboxypeptidase possessed both peptidase and esterase activities and it sequentially hydrolysed amino acids from the carboxyl-terminal end of insulin chain B. It was optimally active at pH 6–7 on peptidase substrates, and at pH 8 on esterase substrates. The enzyme was inhibited by diisopropylfluorophosphate and incorporated 1 mol of DFP-[ 3H]. per mol of enzyme. Both peptidase and esterase activities were strongly inhibited by HgCl 2 but not by p-hydroxymercuribenzoate or iodoacetamide. Carboxypeptidase inhibitor from potatoes did not inhibit the enzyme.

Carboxypeptidase A activity of cultured skin fibroblasts and relationship to cystic fibrosis

Properties of carboxypeptidase A of cultured skin fibroblasts from control and cystic fibrosis patients were studied using α- N-carbobenzoxy- l-glutamyl- l-tyrosine as substrate. Carboxypeptidase A was inhibited by thiomersal, cyanide, iodoacetate and N-ethylmaleimide in a similar manner for control and cystic fibrosis fibroblasts. Both trypsin and dithiothreitol treatment activated the enzyme, but 1,10-phenanthroline inhibited only in the presence of dithiothreitol. Both Zn 2+ and Co 2+ reversed this inhibition. Trypsin treatment of carboxypeptidase A produced a form of the enzyme having a higher k m value for both control and cystic fibrosis fibroblasts. Dithiothreitol treatment of control fibroblasts resulted in a form with similar properties to the trypsin activated form, but cystic fibrosis fibroblasts yielded a variant form with even higher k m and V max values. Since other properties were similar, it seems likely that this difference reflected binding of a molecule to the enzyme rather than of a defect in the enzyme.

発芽ダイズ種子カルボキシペプチダーゼ(第2報) : カルボキシペプチダーゼS<SUB>a</SUB>およびS<SUB>b</SUB>の安定性, 化学的および動力学的性質

発芽ダイズ種子カルボキシペプチダーゼ(第2報) : カルボキシペプチダーゼS<SUB>a</SUB>およびS<SUB>b</SUB>の安定性, 化学的および動力学的性質

Functional and conformational properties of carboxypeptidase A

Abstract