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PubMed1988

Characterization of the carboxypeptidase N secreted by Hep G2 cells.

Human hepatoma (Hep G2) cells secrete nanogram quantities of carboxypeptidase enzymes which are capable of hydrolyzing COOH-terminal lysine and arginine residues. A carboxypeptidase with a neutral pH optimum (greater than pH 7.0) was partially purified from the conditioned medium and compared with pure plasma carboxypeptidase N. The two enzymes behaved in a similar manner on gel filtration (apparent Mr = 280,000), DE52 ion exchange chromatography, and concanavalin A-affinity chromatography and were indistinguishable enzymatically and immunologically. Immunoblots of the Hep G2 and plasma carboxypeptidase N before and following deglycosylation with peptide-N4-[N-acetyl-beta-glucosaminyl]asparagine amidase F revealed a similar, if not identical, multimeric structure. A second carboxypeptidase with a lower molecular weight and a pH optimum of 5.0 was also detected in the Hep G2 medium.

Animals↗

PubMed1988

Dopamine D2 receptor binding subunits of Mr congruent to 140,000 and 94,000 in brain: deglycosylation yields a common unit of Mr congruent to 44,000.

The ligand-binding subunit of the porcine striatal dopamine D2 receptor was identified by photoaffinity labeling with [125I]N-azidophenethylspiperone ([125I]NAPS). Upon photolysis, [125I]NAPS covalently incorporated into a broad band of apparent Mr congruent 140,000 with an appropriate pharmacological profile for D2 receptors as assessed by autoradiography after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Smaller subunits of apparent Mr congruent 94,000 and 34,000 were specifically labeled by [125I]NAPS with an appropriate D2 receptor profile and were similar to the major ligand-binding subunits of photoaffinity-labeled canine striatal D2 receptors. Photoaffinity labeling in the absence or presence of multiple protease inhibitors did not alter the migration pattern of the Mr congruent to 140,000/94,000 subunits upon denaturing electrophoresis in either the absence or presence of thiol-reducing/alkylating reagents. In order to investigate the possible basis for the existence of these high molecular weight forms of the D2 receptor, we assessed the carbohydrate nature of photolabeled D2 ligand-binding subunits by the use of lectin affinity chromatography and specific exo- and endoglycosidase treatments. Both photoaffinity-labeled D2 receptor proteins from porcine striatum (Mr congruent to 140,000 and 94,000) were glycoproteins as indexed by their absorption and specific elution from wheat germ agglutinin lectin resins. The exoglycosidase neuraminidase altered the electrophoretic mobility of both the Mr congruent to 140,000 and 94,000 labeled subunits to a single band of apparent Mr congruent to 51,000. Prior removal of sialic acid residues did not alter the reversible binding characteristics of [3H]spiperone to D2 receptors. Complete removal of receptor-associated N-linked carbohydrate by the endoglycosidase glycopeptidase F (peptide-N4[N-acetyl-beta-glucosaminyl]asparagine amidase) produced a further increase in the mobility of the Mr congruent to 51,000 subunit to apparent Mr congruent to 44,000. The porcine Mr congruent to 34,000 photolabeled peptide is an N-linked glycoprotein as assessed by lectin affinity chromatography and susceptibility to digestion by glycopeptidase F to a peptide of apparent Mr congruent to 23,000.(ABSTRACT TRUNCATED AT 400 WORDS)

Affinity Labels↗

PubMed1978

Subcellular fractionation studies on peroral jejunal biopsies from the dog.

Portions of closed jejunal biopsies from the dog were homogenised and their organelles separated by isopycnic centrifugation on continuous sucrose density gradients. The distributions of marker enzymes for the principal organelles were determined using highly sensitive assay procedures. The following organelles, with assayed marker enzymes and modal densities between brackets were characterised: peroxisomes (catalase, 1.21); brush borders (zinc-resistant alpha-glucosidase, leucyl-beta-naphthyl-amidase, gamma-glutamyl transferase, alkaline phosphatase, 1.20); lysosomes (N-acetyl-beta-glucosaminidase, alpha-mannosidase, 1.19); mitochondria (malate dehydrogenase, 1.18); endoplasmic reticulum (Tris-resistant alpha-glucosidase, 1.16); basal-lateral membranes (5'-nucleotidase, 1.11) and cytosol (lactate dehydrogenase). Homogenisation in isotonic sucrose containing digitonin (0.12 mmol/litre) selectively disrupted lysosomes and increased the equilibrium density of brush border and basal-lateral membranes. This procedure will be used to study the subcellular pathology of naturally occurring intestinal disease in the dog.

Acetylglucosaminidase↗

PubMed1988

Deglycosylation of fibrinogen accelerates polymerization and increases lateral aggregation of fibrin fibers.

Fibrinogen, the major structural precursor of blood clots, was deglycosylated by peptide-N-(N-acetyl-beta-glucosaminyl)asparagine amidase without denaturation of the polypeptide chains. Deglycosylated fibrinogen behaved normally in clinical coagulation assays, although it is less soluble than normal fibrinogen. However, the turbidity of clots formed from deglycosylated fibrinogen always rose faster and higher than that of clots from normal fibrinogen. Scanning and transmission electron microscopy demonstrated that fibrin made from clots of deglycosylated fibrinogen consisted of thicker, less-branched fiber bundles in a more porous network. Moreover, the degree of lateral aggregation was directly related to clot turbidity and inversely related to branching. Deglycosylation promoted turbidity development, lateral aggregation, and porosity of clots under all conditions tested. All other steps in the coagulation pathways appeared to be unaffected by the absence of carbohydrate. These results suggest that carbohydrate constitutively affects the behavior of deglycosylated fibrinogens by 1) contributing a repulsive force that promotes fibrinogen solubility and limits fibrin assembly and 2) sensitizing fibrin to conditions that influence assembly and clot structure.

Factor XII↗

PubMed1986

The use of normal filter paper for "dot-immunobinding assay" of some antibodies.

Normal filter papers were used for specific detection of tiny amounts of antibodies against two penicillin amidase molecular forms from Escherichia coli, monoclonal antibodies of IgG and IgM class against lipopolysaccharide from Citrobacter O36 and IgM antibody against glycoprotein N from human red blood cells. For colour detection of antibodies bound to proper antigens adsorbed on the paper, second antibody-horse radish peroxidase conjugates and hydrogen peroxide with 4-chloronaphthol were applied. The use of filter paper for dot-immunobinding assay of antibodies gave similar results to those obtained with expensive nitrocellulose sheets used by other authors.

Antibodies↗

PubMed1987

205Tl+ as a spectroscopic probe of the monovalent cation binding sites of bovine plasma activated protein C and des-1-41-light-chain-activated protein C.

The kinetic properties of the stimulation by Tl+ of the amidase activity of bovine plasma activated protein C (APC) and a limited-proteolytic derivative of this enzyme, des-1-41-light chain APC (GDAPC), which has no remaining gamma-carboxyglutamic acid residues, have been compared, along with a 205Tl+ NMR analysis of the interaction of this cation with these enzymes, at 6 degrees C. In contrast to other monovalent cations, the productive kinetic complex of Tl+ and APC involves only a single Tl+ site, or class of sites, and is similar to GDAPC in this regard. In the case of each enzyme, the kinetic mechanism that best describes the participation of Tl+ is a rapid equilibrium type with random addition of the cation and substrate to the enzyme. The dissociation constants of the Tl+ X APC and Tl+ X GDAPC complexes have been determined by NMR analysis and have been found to be very similar to the same constants as calculated by kinetic means. These cation sites are also present intact on each zymogen, demonstrating that they are not generated as a result of activation. Our results also show that the Ca2+ binding sites of these proteins are exclusive of the T1+ site and that some interference with Tl+ binding is exercised by an active site-directed affinity label. We conclude that Tl+ can be effectively employed as a spectroscopic probe of the monovalent cation sites that serve an extensive stimulatory role in the amidolytic and esterolytic activities of APC.

Affinity Labels↗

PubMed1986

Isolation and characterization of a thrombin-like enzyme from the venom of Crotalus durissus terrificus.

A thrombin-like enzyme was isolated in 6% yield from the venom of Crotalus durissus terrificus by ammonium sulfate precipitation followed by gel filtration on Sephadex G-75 and finally affinity chromatography on Sepharose-1,4-butanediol-diglycyl-p-aminobenzamide eluted with 0.15 M benzamidine. The enzyme behaved like a single component on SDS-PAGE corresponding to a molecular weight of 34 kDa. The specific activity of the enzyme toward bovine fibrinogen was 71 NIH U/mg protein. The pH optimum for the coagulation of human fibrinogen was 8.0. The enzyme hydrolyzes the alpha-chain of fibrinogen, has amidase activity on L-arginine-p-nitroanilide and L-arginine-7-amido-4-methyl-coumarin amino terminal blocked peptides and presents esterolytic activity on N-alpha-tosyl-L-arginine-methylester.

Blood Coagulation↗

PubMed1986

[Various properties and kinetics of interaction of high and low molecular weight human kininogens with human plasma kallikrein].

A relatively simple procedure for isolation and purification of human blood plasma kallikrein (HPK) by QAE-Sephadex A-50 SP-Sephadex C-50 and affinity chromatography on Sepharose 4B with immobilized soybean trypsin inhibitor with the activity yield of about 40% has been developed. The method allows for simultaneous isolation of low (LMW) and high molecular weight (HMW) kininogens from the same HPK sample. HPK preparations are homogeneous upon 7.5% polyacrylamide gel electrophoresis in the presence of 0.1% SDS; its Mr is 90,000. After treatment with beta-mercaptoethanol, HPK dissociates into two fragments with Mr of 43,000 and 37,000. HPK preparations have high specific activities of esterase (31 microM/min), amidase (78 microM/min), and kininogenase (420 micrograms equiv. bradikinin/min). The high degree of protein purification was demonstrated by titration of active centers with 4-methylumbelliferylguanidine benzoate. The values of equilibrium dissociation constants for the HPK complex with aprotinin (Ki) equal to 1 X 10(-8) M (ethyl ester of N-alpha-benzoyl-L-arginine) and 1,5 X 10(-9) M (HMW) were determined. The kinetics of HPK-induced liberation of bradikinin from purified preparations of HMW and LMW was studied. The kinetic parameters (Km, kcat and kcat/Km) of this reaction suggest a high affinity of HPK for HMW, but not for LMW. LMW does not compete with HMW for the enzyme active center. It is assumed that LMW is not a physiological substrate for HPK.

Bradykinin↗

PubMed1987

Ligands which effect human protein C activation by thrombin.

This report documents attempts to mimic the rate enhancement effect of thrombomodulin on human alpha-thrombin-catalyzed activation of human protein C in the absence of exogenous calcium. Specifically the following tryptamine analogs at 1 mM concentration were shown to enhance the protein C activation rate relative to a control with no added effector at pH 8.3 (50 mM Tris-HCl, 0.1 M NaCl, 37 degrees C): serotonin, 1.2; tryptamine, 2.9; 5-fluorotryptamine, 4.4; 6-fluorotryptamine, 7.2. At much higher levels, e.g. 10 mM, all of the above effectors, as well as indole, showed a moderate inhibition of human protein C activation. ATP, a platelet release product, showed a sigmoidal inhibition pattern similar to that found previously for thrombin amidase, clotting, and esterase activity (Conery, B.G., and Berliner, L.J. (1983) Biochemistry 22, 369-375). Overall, the enhancement factors for human alpha-thrombin activation of protein C with the tryptamine analogs described above were remarkable when considering the effect of a simple ligand versus the natural activator, thrombomodulin.

Adenosine Triphosphate↗

PubMed1986

[Effect of reduction of the interchain disulfide bridge of human thrombin on its enzymatic activity and structure].

It was shown that selective hydrolysis of the disulfide bridge between the A- and B-chains of human thrombin in the absence of denaturating agents decrease its proteolytic (e.g., fibrinogen-binding), esterase and amidase activities. Both chains remain bound by non-covalent interactions. A preparation of partially reduced thrombin was obtained and its kinetic parameters were determined. The experimental results suggest that the S-S bond connecting the A- and B-chains of thrombin is involved in the stabilization of the enzyme active center.

Chromatography, Gel↗

PubMed1986

Phenylpyruvate-specific glutamine transaminase and renal ammoniagenesis.

The glutaminase II ammoniagenic pathway is composed of two enzymes, glutamine transaminase (GTA) and omega-amidase. Studies herein reported define the basal activity, intrarenal distribution and response to chronic acidosis of the more active renal isoenzyme of GTA. A gradient of diminishing enzyme activity was found in assays of cortical, medullary and papillary sections (GTA activity, cortex 114 +/- 3 mumol/g/h; outer medulla 20 +/- 0.6 mumol/g/h; papilla 3 mumol/g/h). Dog kidney had much less activity while no GTA activity was found in guinea pig kidneys. In vitro acidification enhanced ammonia production by the glutaminase II pathway when studied in cytosolic preparations made from normal rat cortex. Chronic in vivo metabolic acidosis increased rat renal cortical and medullary but not papillary GTA activity by 16 and 12%, respectively. Incubation of cortical cytosolic extracts from chronically acidotic rats at pH 7.4 revealed a 29% increase in ammoniagenesis via glutaminase II, as compared to extracts from non-acidotic control rats. The cortical concentration of the most active substrate of GTA phenylpyruvate, is 343 +/- 12 mumol/kg fresh weight and its level was not influenced by in vivo acidosis. Additional studies are presented which suggest that a functional link may exist between glutaminase II and glutamate oxalacetate transaminase. This linkage could result in the cyclic utilization and reformation of phenylpyruvate while glutamine is progressively deamidated and free ammonia formed. The physiologic implications of these results are discussed.

Ammonia↗

PubMed1985

[The kinetics of hydrolysis of alanine peptide esters and -p-nitroanilides by thermitase, a thermostable serine protease from Thermoactinomyces vulgaris: secondary specificity, influence of temperature and solute].

The kinetic parameters Km and kcat and the resulting proteolytic coefficients kcat/Km for the hydrolysis of blocked alanine peptide esters (X(Ala)nOMe) and -p-nitroanilides (X(Ala)n-pNA) of variable length (n = 1 to 5 alanine residues) by the cationic, microbial serine protease thermitase are determined in order to delineate the number of subsites involved in catalysis. Thermitase has at least five secondary subsites (S1 to S5) being hydrophobic in S1 to S4. Arrhenius plots for both, esterase and amidase activity were biphasic with a break at 30 degrees C, followed by a downward bend. The influence of dimethylformamide, solute for many substrates, on the thermitase-catalyzed esterolysis of Z(Ala)2OMe was also investigated. In contrast to the kcat values being unaffected by 5 to 30% dimethylformamide, the Km values increased logarithmically with enhancing its concentration.

Alanine↗

PubMed1985

Enzymes of vitamin B6 degradation. Purification and properties of two N-acetylamidohydrolases.

alpha-(N-Acetylaminomethylene)succinic acid hydrolase (Compound A hydrolase, EC 3.5.1-) and alpha-hydroxymethyl-alpha'-(N-acetylaminomethylene)succinic acid hydrolase (Compound B hydrolase, EC 3.5.1-) were purified to homogeneity from Pseudomonas MA-1 and Arthrobacter Cr-7, respectively. The two inducible enzymes catalyze Reactions 1 and 2, respectively, which release the first generally useful anabolic intermediates during growth of these organisms with (formula; see text) pyridoxine as a sole source of carbon and nitrogen. Compound A hydrolase is a monomeric protein of Mr 32,500 with aspartic acid as its NH2-terminal residue. Compound B hydrolase (Mr congruent to 205,000) is a multimer containing probably six identical subunits with glycine as the NH2 terminus. The two enzymes have quite different amino acid analyses, although both are high in Asx and Glx, lack tryptophan, and show similar stabilities to pH and temperature. Compound A hydrolase has a pI of 4.4, a Km of 3.3 microM, and a Vmax of 3.1 mumol X min-1 X mg-1 at pH 6.5 and 25 degrees C; no analogue substrates were found. Compound B hydrolase has a pI of 4.2, a Km of 25 microM, and a Vmax of 3.8 mumol X min-1 X mg-1 at 25 degrees C and pH 7.0; it also hydrolyzes Compound A slowly. Both enzymes are inhibited competitively by di- and tricarboxylic acids, itaconic acid being among the most effective. Sulfite inhibits both enzymes by a time-dependent mechanism not yet understood. The two amidases appear to differ greatly in architecture despite the similarity in properties and in the overall reactions they catalyze.

Amidohydrolases↗

PubMed1985

Characterization of the platelet aggregation inducer and inhibitor from Echis carinatus snake venom.

Echis carinatus venom was separated into twenty fractions by means of ultrafiltration and CM-Sephadex C-50 column chromatography. Fraction II possessed inhibitory activity on the aggregation of washed rabbit platelets and fraction XII possessed the procoagulant and platelet aggregation-inducing activity. Both were further purified by gel filtration on a Sephacryl S-200 column. The purified aggregation inducer was a glycoprotein with procoagulant activity 10-12-times that of the crude venom. It possessed proteinase and amidase but was devoid of esterase activity. The molecular weight was 16 000, and it contained 8.7% of neutral sugar. The isoelectric point was pH 7.6. The purified aggregation inhibitor was a single peptide chain with a molecular weight of 6800 and contained 22.1% of neutral sugar. The isoelectric point was pH 4.8. It was devoid of any enzymatic activity of the crude venom. The IC50 was about 10 micrograms/ml on the thrombin-induced platelet aggregation. The inhibitory activity was fully retained after the treatment of the venom aggregation inhibitor with neuraminidase, but was completely destroyed by sodium metaperiodate. Upon heat treatment at 90 degrees C, the venom aggregation inhibitor was heat stable at pH 5.5 for 4 h, but was completely destroyed after 2 h at pH 8.9 and retained about 50% of its inhibitory activity of the control at pH 7.2 for 4 h. The venom aggregation inhibitor decreased the elasticity of the whole blood clot, and this effect was related to its inhibitory action on platelet aggregation instead of blood coagulation.

Amino Acids↗

PubMed1979

[Nicotinamidase and the so-called pyrazinamidase in mycobacteria; the simultaneous occurrence of both activites (author's transl)].

Nicotin- and the so-called pyrazinamidase (in the following: "pyrazinamidase") have been found in strains of four mycobacteria species, M. fortuitum, M. gastri, M. bovis and M. microti. These findings are in contradiction to those summarized in Bergey's Manual of Determinative Bacteriology (1974). The reason for the discrepancies is that the original method (Bönicke, 1961) for amidase determination has not taken the following aspects into consideration: a) The inducibility of the nicotin- and "pyrazinamidase" (example: M. fortuitum); b) The temperature sensitivity of these enzymes (M. gastri); c) The light sensitivity of nicotinamidase (in photochromogenic M. gastri strains); d) The optimal substrate concentration which must be at least 4 mM instead of 0,8 mm. The following consequences can be drawn for the taxonomy and biochemistry of the tested organisms: e) The species status of M. gastri should be annuled. The main difference between M. gastri and M. kansasii consists only of the non-agglutinability of M. gastri by anti-M. kansasii serum. "Pyrazinamidase" and also nitrate reductase (Tarnok et al., in press) are positive in strains of both species; f) M. bovis possesses nicotin- and "pyrazinamidase" as M. tuberculosis too. Thus, these two species are more closely related than suggested earlier; g) Till now, no Mycobacterium has been found showing nicotinamidase without "pyrazinamidase" activity (or vice versa). It seems to be very probable that nicotinamidase, an enzyme of low substrate specificity, is able to hydrolyze several compounds with a nicotinamide-like structure such as pyrazinamide. Thus, we suggest the annulment of the term pyrazinamidase or the employment of quotation marks ("pyrazinamidase") to show the fictitious value of this designation.

Amidohydrolases↗

PubMed1979

Fujiwara trait: the first case of kininogen deficiency in Japan.

Asymptomatic identical twins were found to show the prolonged activated partial thromboplastin time, which was corrected by addition of normal, Hageman factor deficient or Fletcher trait plasma but not corrected by Fitzgerald or Williams plasma. The prolonged activated partial thromboplastin time was also corrected by addition of highly purified bovine high molecular weight kininogen but not by low molecular weight kininogen. When total kininogen was measured as the amount of bradykinin released by trypsin on acid treated plasma, only trace amount was detected in Fujiwara and Williams plasmas, although Fitzgerald plasma showed approximately 50% of the total kininogen of normal plasma level. Acetone-kaolin activated amidase activity of plasma kallikrein was not generated by Fujiwara plasma. Substitution with normal plasma in various ratios showed plasma kallikrein activity proportionally to the normal plasma contents. Extrapolation with the values at 120 min after activation gave the prekallikrein content of Fujiwara plasma as 30% of the normal value.

Diseases in Twins↗

PubMed1975

Substrate specificity of carboxypeptidase from Watermelon.

The substrate specificity of carboxypeptidase (F-II) purified from watermelon for various synthetic peptides and esters was examined kinetically. The enzyme showed a broad substrate specificity against various carbobenzoxy- and benzyl-dipeptides. Peptides containing glycine or proline were hydrolyzed slowly by the enzyme. Peptides containing hydrophobic amino acids were hydrolyzed rapidly. The presence of hydrophobic amino acid residues, not only at the C-terminal position but also at the second position and probably the third position from the C-terminal resulted in an increase in the rate of hydrolysis. Inhibition studies with diisopropyl flurophosphate and diastereomers of carbobenzoxy-Phe-Ala demonstrated that the peptidase and esterase activities of the enzyme are both catalyzed by the same site of the enzyme molecule, but the binding sites for peptides and esters seem not to be the same. The enzyme also had amidase activity, which was optimal at pH 7.0.

Amidohydrolases↗

PubMedDate not supplied

Investigation of the interaction of trypsin with heparin.

The reversible inhibition of the enzymatic activity of trypsin by heparin was investigated. On the basis of an analysis of the Lineweaver-Burk and Dixon graphs, a noncompetitive nature of the inhibition of the BAPA amidase activity of trypsin by heparin was detected, and the values of Km and Ki were determined, equal to 3.1 . 10(-4) and 3.7-3.9 . 10(-7) M, respectively. A comparison of these values indicates a great affinity of heparin for the enzyme. It was shown that heparin inhibits the BAEE esterase activity of trypsin and at the same time has no inhibiting effect on acetyltrypsin. Considering that the acetylation of trypsin leads to selective blocking of the epsilon-amino groups, it was concluded that the epsilon-amino groups of the lysine residues of the trypsin molecule participate in the interaction with heparin.

Catalysis↗