Specificity of proteolysis inhibitors in rabbit plasma

Hydrolysis and inhibition of hydrolysis of leucine enkephalin in Oryctolagus plasma were studied by kinetics and chromatographic techniques. By data obtained, in this species, enkephalins are degraded by the same enzymes active in other mammals: aminopeptidases, dipeptidylaminopeptidases, and dipeptidylcarboxypeptidases. At variance with data obtained in other species, where enkephalins are hydrolyzed mostly by aminopeptidases, in Oryctolagus Leu-enkephalin hydrolysis is mainly due to dipeptidylcarboxypeptidases, whereas aminopeptidases contribution is the minimum of all three enzyme groups. Comparative analyses performed in the presence and in the absence of plasma inhibitors indicate that the ability of these substances to reduce substratum hydrolysis is very limited. On the contrary, the specific hydrolysis pattern evidenced appears to originate primarily from selective inhibition of the three groups of enzymes. Results obtained appear consistent with a role of plasma inhibitors in tuning hydrolysis to specific substrata, without appreciably modifying the amount of the substratum degraded.

Cloning and characterization of the Pichia pastoris PRC1 gene encoding carboxypeptidase Y

We purified a 58 kDa serine protease from culture-supernatant of Pichia pastoris and found that the NH2-terminal amino acid sequence of this protease is closely homologous to that of mature protein of Saccharomyces cerevisiae carboxypeptidase Y (CPY), which is encoded by the PRC1 gene. Using the S. cerevisiae PRC1 gene as a hybridization probe, a cross-hybridizing fragment of P. pastoris genomic DNA was identified and the gene, PRC1, encoding CPY, was cloned. The open reading frame of the P. pastoris PRC1 gene consists of 1569 bp encoding a protein of 523 amino acids. The molecular mass of the protein is calculated to be 59.44 kDa without sugar chains. The protein comprises 20 amino acids of pre (signal)-peptide, 87 amino acids of pro-peptide and 416 amino acids of mature peptide, and has four N-glycosylation sites. The NH2-terminal amino acid sequence of mature peptide is completely identical with that of the protease purified from the culture-supernatant. There is 61% identity between the amino acid sequences of P. pastoris Prc1p and S. cerevisiae Prc1p. Chromosomal disruption of the PRC1 gene resulted in the loss of CPY activity. Over-expression of the PRC1 gene under regulation of the P. pastoris AOX1 promoter resulted in accumulation of a large amount of active CPY in the intracellular fraction, and secretion of a slightly larger molecule that is thought to be pro-CPY. The nucleotide sequence data reported in this paper will appear in the EMBL Nucleotide Sequence Databases under the Accession Number X87987.

[Partial characteristics of the basic phenylmethylsulfonylfluoride-inhibited carboxypeptidase from cat brain]

Cat brain carboxypeptidase releasing C-terminal arginine from the synthetic substrate, dansyl-Phe-Leu-Arg, was partially characterized. The enzyme has a molecular weight of 100-120 kDa, displays the maximal activity at pH 6.0-6.5 and is strongly inhibited by phenylmethanesulfonylfluoride and 4-chloromercuribenzoate, less strongly (by 40%) by iodoacetamide and is not inhibited by N-ethylmaleimide, 2-mercaptoethanol, EDTA, Co2+ and guanidinoethylmercaptosuccinic acid. The Km values for the hydrolysis of dansyl-Phe-Leu-Arg and dansyl-Phe-Ala-Arg by soluble carboxypeptidase are 48 and 96 microM, respectively. By all properties, this carboxypeptidase differs from other known carboxypeptidases. Possible participation of the enzyme in neuropeptide metabolism is discussed.

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.

Production and utilization of detyrosinated tubulin in developing Artemia larvae: evidence for a tubulin-reactive carboxypeptidase

The reversible, enzymatically driven removal and readdition of its carboxy-terminal tyrosine are major posttranslational modifications of alpha-tubulin. To study these processes isoform-specific antibodies were produced and subsequently used to characterize tyrosinated and detyrosinated tubulin in the brine shrimp, Artemia. Tyrosinated tubulin existed in relatively constant amounts on western blots of cell-free protein extracts from Artemia at all developmental stages examined, whereas detyrosinated tubulin was present after 20-24 h of postgastrula growth. In agreement with the blots, the detyrosinated isoform was observed in immunofluorescently stained larvae after 24 h of incubation, appearing first in structures of a transient nature, namely spindles and midbodies. The elongated muscle cells encircling the gut and the epithelium bordering the gut lumen were stained extensively with antibody to detyrosinated tubulin. Detyrosination was accompanied by the appearance of a tubulin-reactive carboxypeptidase, which used both nonpolymerized and polymerized tubulin as substrate. The enzyme bound to microtubules very poorly, if at all, under conditions used in this work. Several inhibitors of carboxypeptidase A had no effect on the carboxypeptidase from Artemia and revealed similarities between this enzyme and others thought to be tubulin specific. The use of inhibitors also indicated that the carboxypeptidase from Artemia recognized aspects of tubulin structure in addition to the carboxy-terminal tyrosine. Our results support the idea that detyrosinated tubulin appears in microtubules of varying stability, and they demonstrate that Artemia possess a carboxypeptidase with the potential to detyrosinate tubulin during growth of larvae.

Characterization of the deamidase enzyme responsible for the metabolism of the anticancer peptide: H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2

H-Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH2, a broad spectrum neuropeptide growth factor antagonist (antagonist G), is soon to enter a phase I clinical trial for the treatment of small-cell lung cancer (SCLC). The pre-clinical pharmacology of this peptide has revealed that its metabolism proceeds from the C-terminus via deamidation. In this study the class of enzyme responsible for the degradation of antagonist G has been characterized. Tissue distribution studies on the enzyme have shown it to be very widespread with high specific activity being detected in the spleen, kidney, H69 SCLC xenograft and liver (12.64, 9.58, 8.00 and 6.94 nmols G/mg protein/hr, respectively). HPLC gel filtration indicated that the G-deamidase enzyme had an apparent molecular mass of 81 kDa. The sub-cellular distribution of the enzyme using differential centrifugation indicates that it is largely soluble with > 85% of the activity located in the cytosolic fraction. The distribution of activity towards antagonist G closely resembles that of esterase and acid carboxypeptidase activity, two activities, along with deamidase activity, known to be possessed by serine carboxypeptidases. Studies using a range of protease inhibitors showed clear inhibition of metabolism by phenylmethylsulphonylfluoride and benzyloxycarbonylphenylalanine chloromethylketone, indicating that the enzyme is a chymotrypsin-like serine carboxypeptidase. This knowledge of the enzyme will be invaluable in the further development of antagonist G and similar compounds. Moreover, the widespread distribution of this enzyme together with its broad specificity for C-terminal group suggests that it should be given serious consideration when designing C-terminally modified peptide drugs.

Purification and characterization of TAFI, a thrombin-activable fibrinolysis inhibitor

Previous studies demonstrated that tissue plasminogen activator-induced fibrinolysis in vitro is retarded in the presence of prothrombin (II) activation and that the anticoagulant-activated protein C appears profibrinolytic by preventing the formation of thrombin (IIa)-like activity during fibrinolysis. To disclose the molecular connection between the generation of IIa and the inhibition of fibrinolysis, a lysis assay that is sensitive to the antifibrinolytic effect of II activation was developed and was used to purify a 60-kDa single-chain protein from human plasma. Because the lysis of a clot, produced from purified components, is retarded when this protein is present and when II activation occurs in situ, the protein was named TAFI (thrombin-activatable fibrinolysis inhibitor). TAFI is cleaved by IIa yielding 35-, 25-, and 14-kDa products. Amino-terminal sequence analyses identified TAFI as a precursor of a plasma carboxypeptidase B (CPB). Formation of the 35-kDa product correlates with both prolongation of lysis time and CPB-like activity. Prolongation of lysis time saturates at about 125 nM TAFI. Activated TAFI inhibits the activation of Glu-plasminogen but does not prolong the lysis of clots formed in the presence of Lys-plasminogen. 2-Guanidinoethylmercaptosuccinic acid, a competitive inhibitor of CPB, completely inhibits prolongation of lysis by activated TAFI in a purified system and the prolongation induced by II activation in barium-adsorbed plasma. This suggests that TAFI accounts for the antifibrinolytic effect that accompanies prothrombin activation and that activated protein C appears profibrinolytic by attenuating TAFI activation.

Calcium- and pH-dependent aggregation of carboxypeptidase E

Carboxypeptidase E (CPE) is involved with the biosynthesis of numerous peptide hormones and neurotransmitters. Several forms of CPE have been previously detected in neuroendocrine cells, including a form which is soluble at pH 5.5 (S-CPE), a form which can be extracted from membranes with 1 M NaCl at pH 5.5 (M1-CPE), and a form which requires both 1% Triton X-100 and 1 M NaCl for extraction from membranes at pH 5.5 (M2-CPE). Like other peptide processing enzymes, CPE is known to be sorted into peptide-containing secretory vesicles of the regulated pathway. One mechanism that has been proposed to be important for sorting of regulated pathway proteins is Ca2+ and pH-induced aggregation. CPE purified from bovine pituitary membranes aggregates at pH 5.5 when the concentration of CPE is 0.3 micrograms/microliters or higher, but not when the concentration is 0.01 microgram/microliters. Aggregation of CPE is pH-dependent, with very little aggregation occurring at pH 6 or above. At pH 5.0-5.5, the M2 form of CPE shows a greater tendency to aggregate than the other two forms. At pH 6, Ca2+ concentrations from 1-30 mM increase the aggregation of M1- and M2-CPE, but not S-CPE. The aggregation of M2-CPE does not explain the apparent membrane binding of this protein since the aggregate is solubilized by 1% Triton X-100 at pH 5.5 or by pH 6.0, whereas M2-CPE is not extracted from membranes under these conditions. Taken together, these results are consistent with a model in which the decreasing pH and increasing Ca2+ levels in the trans Golgi network induce the aggregation of CPE, which contributes to the sorting of this protein into regulated pathway secretory vesicles.

[Isolation and properties of carboxypeptidase from the Kamchatka crab Paralithodes camtshatica]

Homogeneous carboxypeptidase PC from a hematopancreas of kamchatka crab Paralithodes camtshatica was obtained by means of an affinity chromatography on sorbents containing arginine, protamine hydrolysate, and phenylalanine as ligands with an yield 23% and purification degree 37.4. The isolated enzyme has a molecular mass 34 kDa, as evidenced by an SDS-PAGE; pI 3.1; an optimum pH 6.5, as estimated for hydrolysis of Dnp-Ala-Ala-Arg; pH-stability range 5-8 in the presence of Ca2+; a temperature optimum 55 degrees C; and Km 0.4 mM. The carboxypeptidase is activated by Co2+ and Ca2+ ions and is inhibited by EDTA and o-phenanthroline, and therefore, it is a metallocarboxypeptidase. The enzyme can effectively split off C-terminal residues Phe and Tyr, as well as Arg and Lys. Residues Pro, Glu, and Asp cannot be split off, and they stop the cleaving of a preceding bond. Thus, the carboxypeptidase PC of kamchatka crab has a mixed substrate specificity, which is characteristic of carboxypeptidase from crawfish and of microbial carboxypeptidases T and SG. The new carboxypeptidase has an amino acid composition Asp41Thr24Ser22Glu32Pro15Gly32Ala291/2Cys5Val19Met8Ile14Leu20Ty r18Phe8Lys7His4 Arg8Trp4. The N-terminal sequence of the enzyme demonstrate a 40% homology with the N-terminal sequence of carboxypeptidase from crawfish.

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.

Prolylcarboxypeptidase (angiotensinase C): purification and characterization of the enzyme from Xanthomanas maltophilia

Prolylcarboxypeptidase (Angiotensinase C, EC 3.4.16.2) was purified to homogeneity from cell free extracts of Xanthomonas maltophilia by ammonium sulfate fractionation and sequential chromatographies on DEAE-Toyopearl, Sephadex G-150, FPLC-Hiload Superdex 200 pg, and FPLC-Hitrap SP columns, with an activity recovery of 15%. The molecular weight of the enzyme was found to be 330,000 by gel filtration and 83,000 by SDS-PAGE, suggesting a tetrameric form for the native enzyme. It had an optimum pH of 8.5 and stability between pH 8.0 and 11.0. The isoelectric point of the enzyme was 6.6. The enzyme hydrolyzed Pro-X bonds when proline was in the penultimate position from the carboxyl terminal. The enzyme was strongly inhibited by diisopropylfluorophosphate (DFP), while phenylmethylsulfonyl fluoride (PMSF), p-chloromercuribenzoic acid (PCMB), iodoacetamide, and metal chelators had no effect.

Detection of mouse mast cell-associated protease mRNA. Heparinase treatment greatly improves RT-PCR of tissues containing mast cell heparin

The reverse transcriptase polymerase chain reaction (RT-PCR) procedure is markedly inhibited in specimens of blood that contain commercial heparin as an anticoagulant or in cell preparations containing rat or mouse peritoneal mast cells. However, it was not known whether the levels of endogenous, mast cell-associated heparin that are present in some mammalian tissues are sufficient to interfere with the use of RT-PCR in these settings. We show that RT-PCR detects little or no mRNA transcripts for either mast cell-associated products, such as mouse mast cell-associated protease-2 or -4 (MMCP-2 or MMCP-4) or mast cell carboxypeptidase A, or for mast cell-nonspecific products, such as glyceraldehyde 3-phosphate dehydrogenase, in routinely prepared specimens of cells or tissues that include populations of heparin-containing mast cells. However, signals for mast cell-associated or mast cell-nonspecific transcripts can be readily detected in such specimens if they are treated with heparinase before RT-PCR. RT-PCR after heparinase treatment appears to represent an extremely sensitive method for detecting mast cell-associated transcripts in tissue specimens, permitting the identification of transcripts for mast cell-specific proteases in the skin of genetically mast cell-deficient WBB6F1-W/WV mice, a tissue that contains few or no mast cells according to histological analysis.

Characterization of a novel carboxypeptidase produced by the entomopathogenic fungus Metarhizium anisopliae

Preparative isoelectric focusing and gel filtration chromatography were used to purify a carboxypeptidase produced by the entomopathogenic fungus Metarhizium anisopliae during growth on cockroach cuticle. The enzyme was inhibited by diisopropyl fluorophosphate, implying involvement of a serine residue in catalysis. However, the M. anisopliae enzyme differed from most serine carboxypeptidases in also being inhibited by the metal chelator 1,10-phenanthroline and in being a small (30 kDa), basic (pI 9.97) protein with a neutral pH optima (pH 6.8). These properties resemble those exhibited by some metalloproteases but the enzyme is not inhibited by Cd2+; nor do Zn2+ or Co2+ restore activity in enzyme inhibited with phenanthroline. The amino-terminal sequence (22 residues) showed no similarity to other protein sequences. Unlike previously reported fungal carboxypeptidases, the M. anisopliae enzyme is powerfully inhibited by potato carboxypeptidase inhibitor. The carboxypeptidase shows a broad primary specificity toward amino acids with hydrophobic side groups in a series of N-blocked dipeptides, with substrates with phenylalanine being the most rapidly hydrolyzed. The S1 subsite also accommodated Glu, confirming its low selectivity. Proline at P1 or P1 resulted in a very poor substrate. The specificity of the carboxypeptidase complements that of the subtilisin-like protease (Pr1) of M. anisopliae. Both Pr1 and the carboxypeptidase are produced during carbon and nitrogen deprivation, which indicates that the exopeptidase functions with Pr1 to degrade peptides to supply amino acids during starvation and pathogenicity.

The expression of serine carboxypeptidases during maturation and germination of the barley grain

cDNA clones encoding three additional serine carboxypeptidases (Ser-CPs) have been isolated from a gibberellic acid-induced barley aleurone cDNA library. The three deduced Ser-CPs belong to the two-chain subfamily of Ser-CPs; they are synthesized as precursors with a putative signal peptide, propeptide, and linker peptide between the A and B chains. Their identification provides the proof for the existence of more than three Ser-CPs in cereal grains, and, based on their sequences, they may exhibit new substrate specificities. The expression of these and of the three previously isolated Ser-CPs from barley grains (CP-MI, CP-MII, and CP-MIII) has been investigated by Northern and Western analysis and RNA PCR. CP-MII is the only Ser-CP to be expressed and accumulate in the developing grain and is stored in its active form in the mature grain. All six Ser-CPs are expressed de novo in the germinating grain, in the scutellum, and/or in the aleurone. Furthermore, at least CP-MI, CP-MII, and CP-MIII are secreted into the endosperm. In addition, all Ser-CPs (except CP-MI) are also expressed in the roots and shoots of the growing seedling. This enzyme family thus appears to be ubiquitous in the barley plant, which suggests that Ser-CPs play additional roles besides their participation in the mobilization of storage proteins.

Carboxypeptidase Taq, a thermostable zinc enzyme, from Thermus aquaticus YT-1: molecular cloning, sequencing, and expression of the encoding gene in Escherichia coli

The gene for carboxypeptidase Taq, a thermostable metallo-carboxypeptidase from Thermus aquaticus YT-1, was cloned and sequenced. The gene comprised an open reading frame of 1,536 base pairs with a GTG initiation codon and a TGA termination codon, which encodes a protein of 56,210 Da consisting of 511 amino acid residues. The GTG initiation codon of the gene was replaced with ATG by site-directed mutagenesis, and then the gene was expressed in Escherichia coli. The enzyme purified from E. coli cells showed the same properties as those of carboxypeptidase Taq prepared from T. aquaticus cells. Analysis for metal ions bound to the enzyme found that one molecule of the enzyme contains one tightly bound zinc ion. Comparison of the entire sequence showed that the enzyme has no obvious sequence similarity to any other metallo-peptidases. However, a His-Glu-X-X-His sequence, which is a conserved sequence in the active site of zinc-dependent endopeptidases and aminopeptidases, was found at positions 276 to 280 of the enzyme. These findings suggest that carboxypeptidase Taq is a novel type of zinc-dependent metallocarboxypeptidase.

Carboxypeptidase U, a plasma carboxypeptidase with high affinity for plasminogen

A novel basic carboxypeptidase clearly different from carboxypeptidase N has been isolated from human plasma. It circulates as an enzymatically inactive precursor enzyme bound to plasminogen. During fibrinolysis, it can be converted to its active form, carboxypeptidase U, through the action of plasmin. The active enzyme has an apparent molecular weight of 53,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It hydrolyzes the synthetic peptides hippuryl-L-arginine and hippuryl-L-lysine but, in contrast to other human basic carboxypeptidases, has only a limited esterase activity. After its activation, carboxypeptidase U tends to be very unstable.

Demonstration of enzyme associations by countermigration electrophoresis in agarose gel

We propose a method to study multienzyme complex formation in vitro based on nondenaturing agarose gel electrophoresis. The enzymes with different isoelectric points (pI) were loaded at the opposite ends of the same lane of agarose gel and electrophoresis was performed at a pH value intermediate between their pI's. In cases where a complex of the enzymes was formed, an additional protein band of low electrophoretic mobility was found corresponding to the point where they crossed on the gel. This band contained both enzyme activities. The method was used to demonstrate association between two enzymes of the mitochondrial citric acid cycle, malate dehydrogenase and citrate synthase, and between the lysosomal hydrolases, beta-galactosidase and cathepsin A. Relative proportions of free and bound enzymes after electrophoresis suggest that interaction between the mitochondrial enzymes is relatively weak compared to that of lysosomal hydrolases. Microdensitometric scanning of countermigration electrophoresis gels was used to determine the stoichiometry of components in the complex.

Identification, purification and partial characterization of a carboxypeptidase from the matrix of rat liver mitochondria: a novel metalloenzyme

A novel carboxypeptidase has been purified to apparent homogeneity from the matrix fraction of rat liver mitochondria by using a procedure mainly based on immobilized-metal-affinity chromatography (IMAC). This carboxypeptidase has been named mCP-III, since it represents the third major peak of carboxypeptidase activity after the IMAC step of purification. mCP-III hydrolyses a number of N-blocked dipeptides, with preference for Cbz-Phe-Ala, and shows no degrading activity towards 125I-casein. The optimal pH of its activity is 7.6, the apparent Km for Cbz-Phe-Ala is 0.12 mM and the specific activity is 145.5 mumol/min per mg of protein. The enzyme is a typical metalloproteinase, is inhibited by 1,10-phenanthroline and carboxypeptidase inhibitor and re-activated by added Zn2+ and Co2+. The molecular mass estimated by molecular-sieve h.p.l.c. was approx. 115 kDa with two protein bands of 61 and 50 kDa shown by SDS/PAGE analysis, indicating that the enzyme is active as a dimer. This is the first clearly identified carboxypeptidase within mitochondria.

Procarboxypeptidase in rat pancreas. Overall characterization and comparison of the activation processes

Three monomeric procarboxypeptidases and a binary complex consisting of a procarboxypeptidase and a chymotrypsinogen have been isolated from rat pancreas by HPLC. N-terminal sequence determination, substrate-specificity analysis and physico-chemical characterization showed that the carboxypeptidase precursors were the A1, A2 and B forms. No isomorphism could be detected for any of these proenzymes and no clear evidence was obtained for the presence of procarboxypeptidase-containing quaternary complexes of the types previously described for other species. Instead, we observed the presence of a binary complex between procarboxypeptidase A2 and chymotrypsinogen B. Among the major pancreatic endoproteinases, only trypsin was found to be a general activator of rat procarboxypeptidases in vitro. Time-course analysis of the products generated after trypsin addition confirmed that full activation of procarboxypeptidase A1 requires several cleavages in the C-terminal region (residues 87-94) of the activation segment, while procarboxypeptidases A2 and B require a single cleavage each. The carboxypeptidases released participate in the trimming of the activation segment in A1 and B, but not in A2, probably because of the high specificity of the latter in the active form.

Ostrich (Struthio camelus) carboxypeptidase A: purification, kinetic properties and characterization of the pancreatic enzyme

1. Carboxypeptidase A beta and carboxypeptidase A tau-type from the pancreas of the ostrich were purified by water extraction of acetone powder, aminobenzylsuccinic acid affinity and hydroxylapatite chromatography. 2. The final preparations were homogeneous when subjected to SDS-PAGE and PAGE. The M(r) values obtained from SDS-PAGE for CPA beta and CPA tau-type were 34,600 and 34,400, respectively. 3. The effects of inhibitors (1,10 phenanthroline and indole-3-acetic acid), pH and temperature on CPA activity were examined. Ki-values for CPI, PPA, D-phe, D-trp and aminobenzylsuccinic acid were determined. 4. Km, kcat and kcat/Km values were determined for hipp-phe, cbz-gly-phe, cbz-(gly)2-phe, cbz-gly-leu, cbz-(gly)2-leu and cbz-(gly)2-val. 5. N-terminal sequencing and amino acid analysis were performed for CPA beta and CPA tau-type.

pH-dependent processing of yeast procarboxypeptidase Y by proteinase A in vivo and in vitro

Carboxypeptidase Y is a vacuolar enzyme from Saccharomyces cerevisiae. It enters the vacuole as a zymogen, procarboxypeptidase Y, which is immediately processed in a reaction involving two endoproteases, proteinase A and proteinase B. We have investigated the in vitro activation of purified procarboxypeptidase Y by purified proteinase A. This has identified two different processing intermediates; one active and one inactive. The intermediates define a 33 amino acid segment of the 91 amino acid propeptide as sufficient for maintaining the enzyme in an inactive state. The inactive intermediate was isolated from a processing reaction at neutral pH. In order to investigate the influence of vacuolar pH on processing in vivo, the autoactivation of proteinase A and its processing of procarboxypeptidase Y were studied in a vma2 prb1 mutant, which is deficient in vacuolar acidification and proteinase B activity. Efficient processing of procarboxypeptidase Y in the absence of proteinase B is dependent on acidic vacuolar pH, and the processing at neutral pH is slow and takes place in two steps similar to those identified in vitro.

Secretion, purification and characterization of a soluble form of the yeast KEX1-encoded protein from insect-cell cultures

The Saccharomyces cerevisiae KEX1 gene encodes a carboxypeptidase involved in the C-terminal processing of the lysine and arginine residues from the precursors of K1 and K2 killer toxins and alpha-factor (mating pheromone). In order to produce large quantities of this unique carboxypeptidase for structural studies, a functional soluble form was obtained by deleting 224 amino acids from the C-terminus of the KEX1-encoded protein which includes a putative membrane-spanning domain. The resulting truncated KEX1 gene (KEX1 delta) has been expressed in the baculovirus/insect cell system. The protein (Kex1 delta p) is efficiently secreted into the culture medium and was purified to apparent homogeneity with a yield of approximately 4 mg/l culture. Kex1 delta p is a glycoprotein with a molecular mass of 56 kDa, its N-terminal sequence is identical to that of the full-length membrane-associated form of the enzyme [Latchinian-Sadek, L. & Thomas, D. Y. (1993) J. Biol. Chem. 268, 534-540], and like the full-length enzyme it is not made as a proenzyme. For the soluble enzyme form, the optimum pH for activity was 5.5-6.0, and the apparent pI value of the protein determined by isoelectric focusing was 4.2. The enzyme cleaves arginine from the C-terminus of the synthetic peptide benzoyl-Phe-Ala-Arg with Km 335 microM and Vmax 282 mumol.min-1 x mg protein-1. Insect-cell-derived Kex1 delta p processes alpha-factor-Lys-Arg, a known natural substrate, to mature active alpha-factor in a manner similar to the membrane-associated full-length enzyme. This secreted form of the enzyme is a convenient source for the isolation of substantial quantities of the pure enzyme for detailed kinetic and structural studies.

Purification and characterization of an endothelin degradation enzyme from rat kidney

A soluble protease which effectively inactivated endothelin-1 was purified 2,700-fold from rat kidney using DE52 anion exchange, concanavalin A-Sepharose, thiopropyl-Sepharose, and Mono P column chromatography. The overall recovery of enzyme activity was 12%. This enzyme appeared to contain two subunits with molecular weights of 34 and 21 kDa. The molecular weight of the active enzyme complex was estimated to be 82 kDa by gel filtration. It was shown to have a pI between 4.8 and 5.2 and a pH optimum of 5.5. Its activity was inhibited by benzyloxycarbonyl-Phe-AlaCHN2 and p-hydroxymercuribenzoic acid, thiol protease inhibitors, and by phenylmethylsulfonyl fluoride, a serine protease inhibitor, but not by metalloprotease inhibitors or other serine protease inhibitors. The purified enzyme degraded endothelin-1 rapidly; KM and Vmax values were 5.9 microM and 0.40 mumol/mg/min, respectively. It removed the carboxyl terminal tryptophan of endothelin-1 by specifically cleaving the Ile20-Trp21 peptide bond, yielding a peptide which was three orders of magnitude less potent than endothelin-1 in causing contraction of porcine coronary arterial rings. In contrast, proendothelin-1 was not degraded by this enzyme. These results are consistent with published findings that show the clearance rate for proendothelin-1 in the pig to be significantly slower than that for endothelin-1. Our study suggests that this enzyme may play a role in the homeostasis of circulating endothelin-1 and contribute to the regulation of vascular tone.

Purification and characterization of the Manduca sexta neuropeptide processing enzyme carboxypeptidase E

The neuropeptide processing enzyme carboxypeptidase E (CPE) (E.C.3.4.17.10) has been well studied in vertebrates but its presence in invertebrates has not yet been reported. CPE activity in insects is present in membrane-bound and soluble forms. The soluble CPE has been purified to homogeneity from the brain of the tobacco hornworm Manduca sexta. It is a 57 kDa glycoprotein containing 9% sugars. It is activated 9.2 +/- 1.8 fold by CoCl2 and inhibited by chelating agents. Its sensitivity to guanidinoethyl-mercaptosuccinic acid, and its molecular mass, make this enzyme a good candidate to be the insect equivalent of the mammalian CPE. Furthermore, its lack of sensitivity towards p-(chloromercuri)benzenesulfonate puts it closer to the vertebrate carboxypeptidase M (CPM). We postulate that insects may possess a single protein fulfilling both CPE and CPM functions.

Novel serine penicillocarboxypeptidase CPD-S3 from Penicillium janthinellum IBT 3991: purification, characterization, and uses in peptide synthesis and modification

A novel carboxypeptidase (CPD-S3) from Penicillium janthinellum IBT 3991 has been isolated in a two-step purification procedure by cation exchange and affinity chromatography. The enzyme is a serine carboxypeptidase with a denatured molecular mass determined by SDS of 62 kDa of which 32% is carbohydrate. The isoelectric point is 5.1. CPD-S3 exhibits a high stability towards organic solvents and elevated temperatures. Besides the carboxypeptidase activity, CPD-S3 exhibits esterase, amidase, and carboxamidohydrolase activities. CPD-S3 favors substrates of L-configuration with basic amino acid residues in either P1 or P1', and particularly dibasic substrates and medium-sized straight-chain alkyl esters for hydrolysis. In aminolysis of esters, amino acid amides and hydrazines coupled in good yield, but methyl esters poorly, and unlike other carboxypeptidases, free amino acids could not be coupled or transpeptidation effected to form amides. In ester semisynthesis, peptides with neutral, but not basic, residues in P1 could be esterified. The scope of applicability for enzymatic peptide synthesis is limited.