Binding of hirudin to human alpha, beta and gamma-thrombin. A comparative kinetic and thermodynamic study

Thermodynamic parameters for the binding of hirudin to human alpha, beta and gamma-thrombin have been determined between pH 5.0 and 9.0, and from 10 degrees C to 40 degrees C; kinetic data for the association and dissociation of the proteinase-inhibitor complex were obtained at pH 7.5 and 21 degrees C. These results have been analysed in parallel with the inhibitor-binding properties of human alpha, beta and gamma-thrombin for the bovine basic pancreatic trypsin inhibitor (Kunitz-type inhibitor; BPTI). For the purpose of an homogeneous comparison, values of the apparent association equilibrium constant for BPTI binding to human gamma-thrombin have been determined between pH 5.0 and 9.0, at 21 degrees C. The different binding behaviour of hirudin and BPTI with respect to human alpha, beta and gamma-thrombin has been related to the inferred stereochemistry of the proteinase-inhibitor contact regions. In particular, whereas the beta and gamma-loops play an appreciable role in the stabilization of the enzyme-hirudin complexes, they contribute to impairment of the adduct formation for the proteinase/BPTI system.

Crystal and molecular structure of the bovine alpha-chymotrypsin-eglin c complex at 2.0 A resolution

The crystal structure of the complex between bovine alpha-chymotrypsin and the leech (Hirudo medicinalis) protein proteinase inhibitor eglin c has been refined at 2.0 A resolution to a crystallographic R-factor of 0.167. The structure of the complex includes 2290 protein and 143 solvent atoms. Eglin c is bound to the cognate enzyme through interactions involving 11 residues of the inhibitor (sites P5-P4' in the reactive site loop, P10' and P23') and 17 residues from chymotrypsin. Binding of eglin c to the enzyme causes a contained hinge-bending movement around residues P4 and P4' of the inhibitor. The tertiary structure of chymotrypsin is little affected, with the exception of the 10-13 region, where an ordered structure for the polypeptide chain is observed. The overall binding mode is consistent with those found in other serine proteinase-protein-inhibitor complexes, including those from different inhibition families. Contained, but significant differences are observed in the establishment of intramolecular hydrogen bonds and polar interactions stabilizing the structure of the intact inhibitor, if the structure of eglin c in its complex with chymotrypsin is compared with that of other eglin c-serine proteinase complexes.

Purification, inhibitory properties and amino acid sequence of a new serine proteinase inhibitor from white mustard (Sinapis alba L.) seed

A new serine proteinase inhibitor, mustard trypsin inhibitor 2 (MTI-2), has been isolated from white mustard (Sinapis alba L.) seed by affinity chromatography and reverse phase HPLC. The protein inhibits the catalytic activity of bovine beta-trypsin and bovine alpha-chymotrypsin, with dissociation constants (Kd) of 1.6 x 10(-10) M and 5.0 x 10(-7) M, respectively, at pH 8.0 and 21 degrees C, the stoichiometry of both proteinase-inhibitor complexes being 1:1. The amino acid sequence of MTI-2, which was determined following S-pyridylethylation, is comprised of 63 residues, corresponding to a molecular weight of about 7 kDa, and shows only extremely limited homology to other serine proteinase inhibitors.

Inhibition of human alpha-, beta- and gamma-thrombin by mono-, bis-, tris- and tetra-benzamidine structures: thermodynamic study

The inhibitory effect of mono-, bis-, tris- and tetra-benzamidine structures (benzamidine, DAPP, TAPB and TAPP, respectively) on the catalytic properties of human alpha-, beta- and gamma-thrombin (alpha-, beta- and gamma-thrombin, respectively) was investigated (between pH 2.0 and 7.0, I = 0.1 M; T = 37.0 +/- 0.5 degrees C). The affinity of DAPP, TAPB and TAPP for alpha- and beta-thrombin is higher than that found for benzamidine association around neutrality, converging in the acidic pH limb; in contrast, benzamidine, DAPP, TAPB and TAPP show the same value of the association inhibition constant (Ki; M-1) for gamma-thrombin over the whole pH range explored. On lowering the pH from 5.5 to 3.0, the decrease in affinity for benzamidine binding to alpha-, beta- and gamma-thrombin, as well as for DAPP, TAPB and TAPP association to gamma-thrombin reflects the acidic-pK shift, upon inhibitor binding of a single ionizing group. On the other hand, values of Ki for DAPP, TAPB and TAPP binding to alpha- and beta-thrombin appear to be modulated by the acidic-pK shift, upon inhibitor association, of two equivalent proton-binding residues over the same pH range. By considering molecular models of the serine proteinase:inhibitor complexes, the observed binding behaviour of benzamidine, DAPP, TAPB and TAPP to alpha-, beta- and gamma-thrombin has been related to the inferred stereochemistry of the enzyme:inhibitor contact region(s).

Assay of 1,4-dioxane in commercial cosmetic products by HPLC

The HPLC assay of 1,4-dioxane in a wide range of commercially available cosmetics containing polyethoxylated surfactants is described. After solid-phase extraction using Bakerbond CN- and Bakerbond C18-cartridges, samples were directly analysed on a LiChrospher CH-8 column with an acetonitrile water eluent and UV detection at 200 nm. Of the total cosmetic products investigated, 48% were found to contain 7.3-85.9 ppm of 1,4-dioxane.

Binding of the recombinant proteinase inhibitor eglin c from leech Hirudo medicinalis to serine (pro)enzymes: a comparative thermodynamic study

The binding of the recombinant proteinase inhibitor eglin c from the leech Hirudo medicinalis to serine (pro)enzymes belonging to the chymotrypsin and subtilisin families has been investigated from the thermodynamic viewpoint, between pH 4.5 and 9.5 and from 10 degrees C to 40 degrees C. The affinity of eglin c for the serine (pro)enzymes considered shows the following trend: Leu-proteinase [the leucine specific serine proteinase from spinach (Spinacia oleracea L.) leaves] greater than human leucocyte elastase congruent to human cathepsin G congruent to subtilisin Carlsberg congruent to bovine alpha-chymotrypsin greater than bovine alpha-chymotrypsinogen A congruent to porcine pancreatic elastase congruent to bovine beta-trypsin. The serine (pro)enzyme-inhibitor complex formation is an entropy-driven process. On increasing the pH from 4.5 to 9.5, the affinity of eglin c for the serine (pro)enzymes considered increases thus reflecting the acid pK shift of the invariant hystidyl catalytic residue from approximately to 6.9 in the free serine proteinases and bovine alpha-chymotrypsinogen A to congruent to 5.1 in the serine (pro)enzyme-inhibitor complexes. Considering the known molecular models, the observed binding behaviour of eglin c was related to the inferred stereochemistry of the serine (pro)enzyme-inhibitor contact regions.

Binding of the recombinant proteinase inhibitor eglin c, of the soybean Bowman-Birk proteinase inhibitor and of its chymotrypsin and trypsin inhibiting fragments to Leu-proteinase, the leucine specific serine proteinase from spinach (Spinacia oleracea L.) leaves: thermodynamic study

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the recombinant proteinase inhibitor eglin c (eglin c), of the soybean Bowman-Birk proteinase inhibitor (BBI) and of its chymotrypsin and trypsin inhibiting fragments (F-C and F-T, respectively) to Leu-proteinase, the leucine specific serine proteinase from spinach (Spinacia oleracea L.) leaves, has been investigated. On lowering the pH from 9.5 to 4.5, values of Ka (at 21 degrees C) for complex formation decrease thus reflecting the acidic pK-shift of the hystidyl catalytic residue from approximately 6.9, in the free Leu-proteinase, to approximately 5.1, in the enzyme: inhibitor adducts. At pH 8.0, values of the apparent thermodynamic parameters for the proteinase:inhibitor complex formation are: Leu-proteinase:eglin c-Ka = 2.2 x 10(11) M-1, delta G degree = -64 kJ/mol, delta H degree = +5.9 kJ/mol, and delta S degree = +240 kJ/molK; Leu-proteinase:BBI-Ka = 3.2 x 10(10) M-1, delta G degree = -59 kJ/mol, delta H degree = +8.8 kJ/mol, and delta S degree = +230 J/molK; and Leu-proteinase:F-C-Ka = 1.1 x 10(6) M-1, delta G degree = -34 kJ/mol, delta H degree = +18 J/mol, and delta S degree = +180 J/molK (values of Ka, delta G degree and delta S degree were obtained at 21.0 degrees C; values of delta H degree were temperature-independent over the range explored, i.e. between 10.0 degrees C and 40.0 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Classic and perinuclear anti-neutrophil cytoplasm antibodies and antimyeloperoxidase antibodies in rapidly progressive glomerulonephritis

Classic anti-neutrophil cytoplasm antibodies (cANCA), perinuclear ANCA (pANCA) and antibodies directed against myeloperoxidase (MPO-Ab) were evaluated in 25 patients with either idiopathic or secondary rapidly progressive glomerulonephritis (RPGN). While cANCA were found almost exclusively in Wegener's granulomatosis, pANCA were detectable in several disorders, including microscopic polyarteritis (mPA), but also idiopathic RPGN. MPO-Ab were frequently found in sera from patients with all types of idiopathic but not of secondary RPGN. These results support the hypothesis that some cases of RPGN are early or limited forms of systematic vasculitis. We then looked for the presence of IgA-ANCA in Henoch-Schoenlein purpura (HSP): we found IgA-ANCA with immunoenzymatic assay but not with immunofluorescence in HSP, in primary IgA-GN and in membranous GN as well, thus suggesting the poor specificity of this type of ANCA. The possible pathologic implications of ANCA were examined in vitro. Serum samples from several patients with ANCA were assessed for their capacity to enhance chemiluminescence generation from resting or PMA-stimulated macrophages. Sera from RPGN and mPA patients displaying anti-MPO activity induced granulocytes to enhance the production of oxygen free radicals, thus suggesting a phlogistic effect of MPO-Ab positive sera.

Binding of the bovine and porcine pancreatic secretory trypsin inhibitor (Kazal) to human leukocyte elastase: a thermodynamic study

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the bovine and porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, PSTI) to human leukocyte elastase has been investigated. At pH 8.0, values of the apparent thermodynamic parameters for human leukocyte elastase: Kazal-type inhibitor complex formation are: bovine PSTI--Ka = 6.3 x 10(4) M-1, delta G degree = -26.9 kJ/mol, delta H degree = +11.7 kJ/mol, and delta S degree = +1.3 x 10(2) entropy units; porcine PSTI--Ka = 7.0 x 10(3) M-1, delta G degree = -21.5 kJ/mol, delta H degree = +13.0 kJ/mol, and delta S degree = +1.2 x 10(2) entropy units (values of Ka, delta G degree and delta S degree were obtained at 21.0 degrees C; values of delta H degree were temperature independent over the range (between 5.0 degrees C and 45.0 degrees C) explored). On increasing the pH from 4.5 to 9.5, values of Ka for bovine and porcine PSTI binding to human leukocyte elastase increase thus reflecting the acidic pK-shift of the His57 catalytic residue from congruent to 7.0, in the free enzyme, to congruent to 5.1, in the serine proteinase: inhibitor complexes. Thermodynamics of bovine and porcine PSTI binding to human leukocyte elastase has been analyzed in parallel with that of related serine (pro)enzyme/Kazal-type inhibitor systems. Considering the known molecular models, the observed binding behaviour of bovine and porcine PSTI to human leukocyte elastase was related to the inferred stereochemistry of the serine proteinase/inhibitor contact region(s).

[Hirudin inhibition of human thrombin activity]

Thermodynamics and kinetics for hirudin binding to human alpha-, beta- and gamma-thrombin, under experimental conditions which mimic the in vivo conditions (i.e., pH = 7.35, T = 37.0 degrees C, I = 0.1 M), indicate that the inhibitor specificity for the three species of the enzyme is different. Such a finding agrees with the human thrombin:hirudin binding geometry as revealed by X-ray crystal studies. From the therapeutic viewpoint, thermodynamics and kinetics here reported indicate that the inhibitory activity of hirudin in vivo is more effective than that shown by antithrombin III, which is generally considered the most important plasma thrombin inhibitor.

Binding of the soybean Bowman-Birk proteinase inhibitor and of its chymotrypsin and trypsin inhibiting fragments to bovine alpha-chymotrypsin and bovine beta-trypsin. A thermodynamic study

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the soybean Bowman-Birk proteinase inhibitor (BBI) and of its chymotrypsin and trypsin inhibiting fragments (F-C(p), F-T(p) and F-T(t), respectively) to bovine alpha-chymotrypsin (alpha-chymotrypsin) and bovine beta-trypsin (beta-trypsin) has been investigated. On the basis of Ka values, the proteinase inhibitor affinity can be arranged as follows: alpha-chymotrypsin: BBI approximately beta-trypsin:BBI approximately beta-trypsin:F-T(t) approximately beta-trypsin:F-T(p) much greater than alpha-chymotrypsin:F-C(p). F-C(p), F-T(p) and F-T(t) do not inhibit beta-trypsin and alpha-chymotrypsin action, respectively. On lowering the pH from 9.5 to 4.5, values of Ka for BBI, F-C(p), F-T(p) and/or F-T(t) binding to alpha-chymotrypsin and beta-trypsin decrease, thus reflecting the acid-pK shift of the invariant His57 catalytic residue from 7.0, in the free enzymes, to 5.2, in the proteinase:inhibitor complexes. Considering the known molecular models, the observed binding behaviour of BBI, F-C(p), F-T(p) and F-T(t) was related to the inferred stereochemistry of the proteinase:inhibitor contact regions.

Bovine trypsinogen activation. A thermodynamic study

The N-alpha-L-isoleucyl-L-valine (Ile-Val) activating dipeptide, sequentially homologous to the Ile 16-Val 17 N-terminus of bovine beta-trypsin, displays an activating effect on equilibria involved in the binding of strong ligands (i.e., n-butylamine and the porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, type I; PSTI)) to bovine trypsinogen. This property has been investigated between pH 3.0 and 9.0 (I = 0.1 M) at 21.0 degrees C. The thermodynamics for the interaction of strong ligands with bovine beta-trypsin has also been studied under the same experimental conditions. The equilibria involved in the binding of the Ile-Val activating dipeptide and/or inhibitors to bovine beta-trypsin and its zymogen are described according to linkage relationships, wherefore interaction(s) between different functional and structural domains of the (pro)enzyme (i.e., the so-called Ile-Val pocket and the primary and/or secondary recognition subsite(s)), possibly involved in the bovine trypsinogen-to-beta-trypsin activation pathway, are considered.

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to human Glu1-, Lys77-, Val442-, and Val561-plasmin: a comparative study

Thermodynamic and kinetic parameters for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to human Glu1-, Lys77-, Val442- and Val561-plasmin (EC 3.4.21.7) have been determined between pH 3.0 and 9.5, and from 5.0 to 45.0 degrees C. The inhibitor-binding properties to human Glu1-, Lys77-, Val442- and Val561-plasmin suggest a possible role of BPTI in modulating plasmin activity when the inhibitor is used therapeutically.

Tumor cell growth inhibition by liposome-encapsulated aromatic polyamidines

Apart from its antiproteinase activity, the aromatic polyamidine TAPP-Br [the bromo derivative of 1,3-di-(p-amidinophenoxy)-2,2-bis-(p-amidinophenoxymethyl)propane (TAPP-H)] is able to inhibit the in vitro growth of a variety of tumor cell lines, including human melanoma, and breast and kidney carcinoma. We have now shown that TAPP-Br can efficiently be encapsulated into egg phosphatidylcholine vesicles. When incorporated into these liposomes, the inhibitory effect of TAPP-Br is significantly enhanced compared with that of the free drug. Based on these promising results, a proposal is made for the delivery of this antiproliferative agent to tumor cells by using liposomes as the vehicle.

X-ray crystal structure of the bovine alpha-chymotrypsin/eglin c complex at 2.6 A resolution

The crystal structure of the molecular complex formed by bovine alpha-chymotrypsin and the recombinant serine proteinase inhibitor eglin c from Hirudo medicinalis has been solved using monoclinic crystals of the complex, reported previously. Four circle diffractometer data at 3.0 A resolution were employed to determine the structure by molecular replacement techniques. Bovine alpha-chymotrypsin alone was used as the search model; it allowed us to correctly orient and translate the enzyme in the unit cell and to obtain sufficient electron density for positioning the eglin c molecule. After independent rigid body refinement of the two complex components, the molecular model yielded a crystallographic R factor of 0.39. Five iterative cycles of restrained crystallographic refinement and model building were conducted, gradually increasing resolution. The current R factor at 2.6 A resolution (diffractometer data) is 0.18. The model includes 56 solvent molecules. Eglin c binds to bovine alpha-chymotrypsin in a manner consistent with other known serine proteinase/inhibitor complex structures. The reactive site loop shows the expected conformation for productive binding and is in tight contact with bovine alpha-chymotrypsin between subsites P3 and P'2; Leu 451 acts as the P1 residue, located in the primary specificity S1 site of the enzyme. Hydrogen bonds equivalent to those observed in complexes of trypsin(ogen) with the pancreatic basic- and secretory-inhibitors are found around the scissile peptide bond.

Determination of 1,4-dioxane in cosmetic products by high-performance liquid chromatography

A rapid high-performance liquid chromatographic procedure has been developed for the assay of 1,4-dioxane in cosmetic products. After solid-phase extraction, using Bond Elut CN and Bond Elut C18 cartridges, samples were analysed directly on a LiChrospher CH-8 reversed-phase column with spectrophotometric detection at 200 nm and acetonitrile - water as eluent. Recovery of 1,4-dioxane from different cosmetic matrices was between 81.5 and 90.1% in the 30-90 microgram g(-1) range. The minimum quantifiable amount was 6.5 microgram g(-1). The method is simple, reproducible and specific and is suitable for routine analyses of commercial cosmetics.

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor) to human and bovine factor Xa. A thermodynamic study

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to human and bovine factor Xa (Stuart-Prower factor; EC 3.4.21.6) has been investigated. Under all the experimental conditions, values of Ka for BPTI binding to human and bovine factor Xa are identical. On lowering the pH from 9.5 to 4.5, values of Ka (at 21.0 degrees C) for BPTI binding to human and bovine factor Xa decrease, thus reflecting the acidic pK shift of the His57 catalytic residue from 7.1, in the free enzyme, to 5.2, in the proteinase-inhibitor complex. At pH 8.0, values of the apparent thermodynamic parameters for BPTI binding to human and bovine factor Xa are: Ka = 2.1 x 10(5)M-1 (at 21.0 degrees C), delta G degree = -29.7 kJ/mol (at 21.0 degrees C), delta S degree = +161 entropy units (at 21.0 degrees C), and delta H degree = +17.6 kJ/mol (temperature-independent over the explored range, from 5.0 degrees C to 45.0 degrees C). Thermodynamics of BPTI binding to human and bovine factor Xa have been analysed in parallel with those of related serine (pro)enzyme/Kazal- and /Kunitz-type inhibitor systems. Considering the known molecular models, the observed binding behaviour of BPTI to human and bovine factor Xa was related to the inferred stereochemistry of the proteinase/inhibitor contact region.

Thermodynamic modeling of internal equilibria involved in the activation of trypsinogen

The effect of activating dipeptides, sequentially homologous to the Ile16-Val17N-terminus of bovine beta-trypsin (beta-trypsin), on equilibria involved in the binding of strong ligands (i.e., n-butylamine, the bovine basic pancreatic trypsin inhibitor (Kunitz-type inhibitor; BPTI) and the porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, type I; PSTI)) to bovine trypsinogen (trypsinogen) was investigated at pH 5.51 (I = 0.1 M) and T = 21.0 +/- 0.5 degrees C; under the same experimental conditions, thermodynamics for the binding of strong ligands to beta-trypsin was also obtained. The equilibria involved in the binding of activating dipeptides and/or inhibitors to beta-trypsin and to its zymogen are described according to an induced-fit formalism, taking into account ligand-linked interaction(s) between different functional and structural domains of the (pro)enzyme possibly involved in the trypsinogen-to-beta-trypsin activation pathway. The analysis of data is focussed on parameters describing interactions between the so-called Ile-Val pocket (where the Ile16-Val17 N-terminus of beta-trypsin or activating dipeptides bind) and the primary and/or secondary recognition subsite(s) (where strong ligands associate) present in the (pro)enzyme. Such an analysis allows to dissect the contributions due to the primary recognition subsite, where small mono-functional ligands (e.g., n-butylamine) bind, from those of the secondary subsite(s), which are additional recognition clefts for macromolecular inhibitors (e.g., BPTI and PSTI).

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to the 33,000 Mr and 54,000 Mr species of human urokinase: thermodynamic study

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to the 33,000 Mr and 54,000 Mr species of human urokinase (EC 3.4.21.31) has been investigated. Under all the experimental conditions, values of Ka for BPTI binding to the 33,000 Mr and 54,000 Mr species of human urokinase are identical. On lowering the pH from 9.5 to 4.5, values of Ka (at 21.0 degrees C) for BPTI binding to human urokinase (33,000 Mr and 54,000 Mr species) decrease thus reflecting the acidic pK-shift of the His-57 catalytic residue from 6.9, in the free enzyme, to 5.1, in the proteinase:inhibitor complex. At pH 8.0, values of the apparent thermodynamic parameters for BPTI binding to human urokinase (33,000 Mr and 54,000 Mr species) are: Ka = 4.9 x 10(4) M-1, delta G degree = -6.3 kcal/mol, and delta S degree = -37 entropy units (all at 21.0 degrees C); and delta H degree = +4.6 kcal/mol (temperature independent over the explored range, from 5.0 degrees C to 45.0 degrees C). Thermodynamics of BPTI binding to human urokinase (33,000 Mr and 54,000 Mr species) have been analyzed in parallel with those of related serine (pro)enzyme Kazal- and /Kunitz-type inhibitor systems. Considering the known molecular models, the observed binding behaviour of BPTI to human urokinase (33,000 Mr and 54,000 Mr species) was related to the inferred stereochemistry of the proteinase/inhibitor contact region.

Liposome-associated retinoic acid. Increased in vitro antiproliferative effects on neoplastic cells

The activity of liposome-associated retinoic acid was analyzed on in vitro cultured tumor cell lines and compared to the antiproliferative effects of free retinoic acid. It was found that liposome-associated retinoic acid is about 300 times more active than free retinoic acid in inhibiting in vitro cell growth of leukemic and melanoma cell lines. An increased activity of retinoic acid (10-20 times) was also obtained after premixing of this compound with empty liposomes, demonstrating that the retinoic acid efficiently interacts with liposomes which may facilitate solubility and cell uptake of retinoids.

Trypsin-like serine proteinase action: determination of the catalytic parameters KS, k+2 and k/3 under conditions where the substrate exceeds the enzyme concentration

A method for the determination of the catalytic parameters Ks, k+2 and k+3 describing trypsin-like serine proteinase action has been developed from the quantitative analysis of the kinetics of hydrolysis of two specific chromogenic substrates, N-alpha-carbobenzoxy-L-arginine p-nitrophenyl ester and N-alpha-carbobenzoxy-L-lysine p-nitrophenyl ester, catalyzed by porcine pancreatic betta-kallikrein B, bovine betta-trypsin and human urokinase (Mr 54,000 species), under conditions where the concentration of the substrate exceeds that of the enzyme. Value of Ks, k+2 and k+3 have been estimated from the effect of substrate concentration on the apparent first-order rate constant of the time-course of the burst phase of p-nitrophenol release preceding the steady-state reaction.

Differential effects of liposome-entrapped desferrioxamine on proliferation and erythroid differentiation of murine erythroleukemic Friend cells

It is known that iron chelators (such as desferrioxamine) are potent inhibitors of both cell proliferation and erythroid differentiation. We have shown with in vitro studies that in the case of tumor cells desferrioxamine is even more efficient in inhibiting cell proliferation when entrapped in liposomes consisting of egg yolk phosphatidylcholine. At the same time liposome-entrapped desferrioxamine retains only a slight effect on hexamethylenebisacetamide induction of erythroid differentiation and hemoglobin accumulation of murine erythroleukemic Friend cells. Based on these findings, we propose liposome-entrapped desferrioxamine as potential antineoplastic agent as well as a specific chemical for the study of both iron metabolism and distribution in normal and neoplastic cells. In addition, unlike free desferrioxamine, the liposome-entrapped drug could also be used in combination with inducers of differentiation. With respect to this issue, it is possible that liposome-entrapped desferrioxamine, might permit erythroid differentiation of both neoplastic cells as well as normal stem cells.

Controlled proteolysis of mouse epidermal growth factor. An RP-HPLC and 1H-n.m.r. study

Tryptic digestion of the mouse epidermal growth factor (mEGF) and the chromatographic separation of its proteolytic fragments by RP-HPLC affords the isolation of the pure hormone, of its 1-48 (Des(49-53)mEGF) and 1-45 (Des(46-53)mEGF) derivatives, and of the carboxyl-terminal pentapeptide W49-W50-E51-L52-R53. Kinetics of mEGF proteolytic degradation follows a two-state time-course: native mEGF being converted into Des(49-53)mEGF with an apparent half-time of 10 min; and Des(49-53)mEGF subsequently hydrolyzed to Des(46-53)mEGF with an apparent half-time of 7 h. Native mEGF and its proteolytic fragments have been characterized by 1H-n.m.r. spectroscopy. In the aromatic and aliphatic regions, the 1H-n.m.r. spectrum proved to be a sufficiently sensitive probe for following controlled proteolysis, and for analyzing the influence of the carboxyl-terminal sequence on the hormone conformation and stability.

Preliminary crystallographic data on the complex of bovine alpha-chymotrypsin with the recombinant proteinase inhibitor eglin c from Hirudo medicinalis

The molecular complex built by bovine alpha-chymotrypsin and the recombinant proteinase inhibitor eglin c from Hirudo medicinalis has been crystallized from polyethylene glycol solutions, using a twofold molar excess of the inhibitor with respect to the serine proteinase. The optimum pH for crystal growth is 6.5. The crystals belong to the monoclinic space group P2(1), with unit cell constant: a = 55.3 A, b = 59.4 A, c = 42.5 A, beta = 99.0 degrees; one complex moiety is present per asymmetric unit. The crystals diffract to 2.0 A resolution and are suitable for detailed X-ray crystallographic investigations.

Inhibition of serine proteinases by p-carbethoxyphenyl esters of epsilon-guanidino- and epsilon-amino caproic acid: thermodynamic and molecular modeling study

The inhibitory effect of the clinically used p-carbethoxyphenyl ester of epsilon-guanidino-caproic acid methanesulphonate (epsilon-GCA-CEP) on the catalytic properties of human LYS77-plasmin (EC 3.4.21.7), bovine factor Xa (EC 3.4.21.6), bovine alpha-thrombin (EC 3.4.21.5), ancrod (EC 3.4.21.28), crotalase (EC 3.4.21.30), bovine beta-trypsin (EC 3.4.21.4), porcine pancreatic beta-kallikrein-B (EC 3.4.21.35), human urinary kallikrein (EC 3.4.21.35) and the Mr 54,000 species of human urokinase (EC 3.4.21.31) was investigated (between pH 2.0 and 8.5, I = 0.1 M; T = 21 +/- 0.5 degrees C), and analyzed in parallel with that of the homologous derivative p-carbethoxyphenyl epsilon-amino-caproate hydro chloride (epsilon-ACA-CEP). On lowering the pH from 5.5 to 3.0, values of the apparent dissociation inhibition constant (Ki) for epsilon-GCA-CEP and epsilon-ACA-CEP interaction with the serine proteinases considered increase, reflecting the acidic pK-shift upon inhibitor binding of a single ionizing group. Over the whole pH range explored, (i) epsilon-GCA-CEP interacts with bovine factor Xa and bovine alpha-thrombin with an higher affinity than that observed for epsilon-ACA-CEP binding; (ii) both inhibitors associate to bovine beta-trypsin with the same affinity; and (iii) epsilon-ACA-CEP inhibits human Lys77-plasmin and the Mr 54,000 species of human urokinase with an higher affinity than that reported for epsilon-GCA-CEP association, thus reflecting the known enzyme primary specificity properties. However, the affinity of epsilon-ACA-CEP for ancrod, crotalase, porcine pancreatic beta-kallikrein-B and human urinary kallikrein, all of which preferably bind arginyl rather than lysyl side chains at the primary position of substrates and/or inhibitors, is paradoxically higher than that displayed by epsilon-GCA-CEP. By considering the amino acid sequences, the X-ray three-dimensional structures and/or the computer-generated molecular models of serine proteinase: inhibitor adducts, the observed binding behaviour of epsilon-GCA-CEP and epsilon-ACA-CEP to the enzymes considered has been related to the inferred stereochemistry of proteinase: inhibitor contact region(s).

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to human alpha-, beta- and gamma-thrombin; a kinetic and thermodynamic study

Kinetic and thermodynamic parameters for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to human alpha-, beta- and gamma-thrombin have been determined, between 5 and 45 degrees C, at pH 7.5. BPTI-binding properties to human thrombins have been analyzed in parallel with those of serine (pro)enzymes acting on cationic and non-cationic substrates, with particular reference to the bovine beta-trypsin/BPTI system. The observed binding behaviour of BPTI to human alpha-, beta- and gamma-thrombin has been related to the inferred stereochemistry of the enzyme/inhibitor contact region(s).

Zymogen activation: effect of peptides sequentially related to the bovine beta-trypsin N-terminus on Kazal inhibitor and benzamidine binding to bovine trypsinogen

The activating effect of peptides sequentially related to the Ile 16-Val17-Gly18 N-terminus of bovine beta-trypsin (namely Ile-Val-Gly, Ile-Val, Ile-Leu, Ile-Ala, Val-Val, Leu-Val, and Val-Leu) on the thermodynamic parameters for the binding of the porcine pancreatic secretory trypsin inhibitor (Kazal inhibitor) and benzamidine to bovine trypsinogen was investigated at pH 5.5 (Bis tris-HCl buffer, I = 0.1 M) and T = 21 +/- 0.5 degrees C. Thermodynamic parameters for Kazal inhibitor and benzamidine association to the binary peptide/zymogen adducts are more favorable than those observed for ligand binding to the proenzyme alone, although never as much as those reported for the formation of bovine beta-trypsin/Kazal inhibitor and bovine beta-trypsin/benzamidine adducts. Analogously, the affinity of activating peptides for the binary proenzyme/Kazal inhibitor and binary proenzyme/benzamidine complexes is higher than that observed for peptide binding to free bovine trypsinogen. Differences in affinity for ligand binding to free bovine trypsinogen, to its binary adducts and to bovine beta-trypsin suggest the presence of different activation levels of the proenzyme, none of which structurally coincide with that achieved in bovine beta-trypsin. The existence of different discrete states suggests that the zymogen-to-active enzyme transition should not be considered as a two-state process but as a multistep event.

Binding of the recombinant proteinase inhibitor eglin c from leech Hirudo medicinalis to human leukocyte elastase, bovine alpha-chymotrypsin and subtilisin Carlsberg: thermodynamic study

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the recombinant proteinase inhibitor eglin c from leech Hirudo medicinalis to human leukocyte elastase (EC 3.4.21.37), bovine alpha-chymotrypsin (EC 3.4.21.1) and subtilisin Carlsberg (EC 3.4.21.14) has been investigated. On lowering the pH from 9.5 to 4.5, values of Ka for eglin c binding to the serine proteinases considered decrease thus reflecting the acid-pK shift of the invariant histidyl catalytic residue (His57 in human leukocyte elastase and bovine alpha-chymotrypsin, and His64 in subtilisin Carlsberg) from congruent to 6.9, in the free enzymes, to congruent to 5.1, in the enzyme:inhibitor adducts. At pH 8.0, values of the apparent thermodynamic parameters for eglin c binding are: human leukocyte elastase - Ka = 1.0 x 10(10) M-1, delta G phi = -13.4 kcal/mol, delta H phi = +1.8 kcal/mol, and delta S phi = +52 entropy units; bovine alpha-chymotrypsin -Ka = 5.0 x 10(9) M-1, delta G phi = -13.0 kcal/mol, delta H phi = +2.0 kcal/mol, and delta S phi = +51 entropy units; and subtilisin Carlsberg - Ka = 6.6 x 10(9) M-1, delta G phi = -13.1 kcal/mol, delta H phi = +2.0 kcal/mol, and delta S phi = +51 entropy units (values of Ka, delta G phi and delta S phi were obtained at 21 degrees C; values of delta H phi were temperature independent over the range explored, i.e. between 10 degrees C and 40 degrees C; 1 kcal = 4184J).(ABSTRACT TRUNCATED AT 250 WORDS)

Aromatic amidines: inhibitory effect on purified plasma serine proteinases, blood coagulation and platelet aggregation

The inhibitory effect of benzamidine as well as of 1,3-di-(p-amidinophenoxy)-2,2-bis-(p-amidinophenoxymethyl)propane (TAPP-H) and TAPP-halo derivatives (with Cl, Br or I) on (i) the catalytic properties of purified plasma serine proteinases (notably, factor Xa, factor VIIa, thrombin and plasmin), (ii) blood coagulation, and (iii) platelet aggregation was investigated in vitro. For all the enzyme/inhibitor systems examined, the inhibition patterns were strictly competitive, and titrations conformed to simple equilibria. The inhibitory effect of TAPP-H and TAPP-halo derivatives is higher, by at least 10-fold, than that of benzamidine, which binds at the primary specificity subsite (S1) of serine proteinases and is commonly taken as a molecular inhibitor model. The high inhibitory effect of aromatic tetraamidines has been interpreted taking into account an additional productive binding for a second benzamidine or halo-benzamidine moiety to the enzyme surface. As a whole, the data reported here indicate that aromatic amidines inhibit the plasma serine proteinases involved in different steps of haemostasis (coagulation and platelet aggregation) as well as clot lysis under physiological-like conditions in vitro.

Interaction of epidermal growth factor with micelles monitored by photochemically induced dynamic nuclear polarization-1H NMR spectroscopy

Photochemically induced dynamic nuclear polarization (CIDNP)-1H-NMR spectroscopy has been used to study the interaction of the protein hormone epidermal growth factor (EGF) with micelles of sodium dodecyl sulfate (SDS) and dodecylphosphorylcholine (DPC). Conventional 1H-NMR spectra show that most protein resonances remain unperturbed when micelles are added to solution, which argues that the overall protein conformation is maintained in the presence of SDS or DPC at the concentrations used. Photo-CIDNP enhancements of resonances assigned to aromatic side chains of residues at the COOH terminus and beta-sheet regions of murine EGF (i.e. Trp-49, Trp-50, and Tyr-37) are considerably reduced in the presence of micelles, while resonances of aromatic side chains of residues found elsewhere on the protein surface are mostly unaffected. This suggests that the primary interaction between murine EGF and the micelle occurs at the micelle-bulk solvent interface. The overall negatively charged surface of SDS micelles tends to induce a stronger interaction with the protein compared to the zwitterionic DPC micelles, probably due to electrostatic interactions. Cleavage of the COOH-terminal pentapeptide containing both tryptophan residues enhances the already present, but weak, interaction with Tyr-10 and attenuates it with Tyr-37. A similar interaction pattern is found with rat EGF suggesting that at least concerning these two species of EGF the interaction is somewhat specific and conserved. A simple mass-action model for protein-micelle interaction is also presented.

Binding of the bovine pancreatic secretory trypsin inhibitor (Kazal) to bovine serine (pro)enzymes

The effect of temperature and pH on the association equilibrium constant (Ka) for the binding of the bovine pancreatic secretory trypsin inhibitor (bovine PSTI, type I; Kazal inhibitor) to bovine beta-trypsin, bovine alpha-chymotrypsin and bovine trypsinogen has been investigated. The results suggest that serine (pro)enzyme inhibitor interaction involves both rigorous spatial configuration and molecular flexibility.

Active-site titration of serine proteinases acting selectively on cationic substrates by N-alpha-carbobenzoxy-L-arginine p-nitrophenyl ester and N-alpha-carbobenzoxy-L-lysine p-nitrophenyl ester; determination of active enzyme concentration

A titration method for determination of trypsin-like serine proteinase concentration has been developed by using ZArgONp and ZLysONp, two specific chromogenic amino-acid derivatives which show the characteristics of optimal active-site titrants. Active proteinase concentration has been estimated from the effect of titrant concentration on the amplitude, at time zero, of the time-course for the instantaneous release of p-nitrophenol, preceding the steady-state reaction (burst phase).

Binding of the Ile-Val and Val-Val effector dipeptides to the binary adducts of bovine trypsinogen with Kunitz and Kazal inhibitors as well as the acylating agent p-nitrophenyl p-guanidinobenzoate. A thermodynamic and kinetic study

Thermodynamics and kinetics of binding of the Ile-Val and Val-Val effector dipeptides to the binary adducts of bovine trypsinogen with the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor), the porcine pancreatic secretory inhibitor (PSTI, Kazal inhibitor) and the acylating agent p-nitrophenyl p-guanidinobenzoate have been investigated at pH 7.4 and 21(+/- 0.5) degrees C. The affinity of both effector dipeptides for bovine trypsinogen: BPTI and bovine trypsinogen: PSTI binary adducts is higher than that observed for the formation of the dipeptide: bovine trypsinogen: p-guanidinobenzoate ternary complexes; moreover, the affinity of Ile-Val for the zymogen binary adducts is higher than that observed for Val-Val association. Binding of Ile-Val and Val-Val to the bovine trypsinogen binary complexes conforms to the induced-fit model, which consists of a fast pre-equilibrium followed by intramolecular isomerization change(s), the latter fast pre-equilibrium followed by intramolecular isomerization change(s), the latter representing the rate-limiting first-order process. For the three bovine trypsinogen systems considered, the rate of the intramolecular isomerization change(s) is essentially independent of the nature of the dipeptide and of the proenzyme binary complex.

The pH dependence of pre-steady-state and steady-state kinetics for the papain-catalyzed hydrolysis of N-alpha-carbobenzoxyglycine p-nitrophenyl ester

Pre-steady-state and steady-state kinetics of the papain (EC 3.4.22.2)-catalyzed hydrolysis of N-alpha-carbobenzoxyglycine p-nitrophenyl ester (ZGlyONp) have been determined between pH 3.0 and 9.5 (I = 0.1 M) at 21 +/- 0.5 degrees C. The results are consistent with the minimum three-step mechanism involving the acyl X enzyme intermediate E X P: (Formula: see text). The formation of the E X S complex may be regarded as a rapid pseudoequilibrium process; the minimum values for k+1 are 8.0 microM-1 s-1 (pH less than or equal to 3.5) and 0.40 microM-1 s-1 (pH greater than 6.0), and that for k-1 is 600 s-1 (pH independent). The pH profile of k+2/Ks (= kcat/Km; Ks = k-1/k+1) reflects the ionization of two groups with pK' values of 4.5 +/- 0.1 and 8.80 +/- 0.15 in the free enzyme. The pH dependence of k+2 and k+3 (measured only at pH values below neutrality) implicates one ionizing group in the acylation and deacylation step with pK'' values of 5.80 +/- 0.15 and 3.10 +/- 0.15, respectively. As expected from the pH dependences of k+2/Ks (= kcat/Km) and k+2, the value of Ks changes with pH from 7.5 X 10(1) microM (pH less than or equal to 3.5) to 1.5 X 10(3) microM (pH greater than 6.0). Values of k-2 and k-3 are close to zero over the whole pH range explored (3.0 to 9.5). The pH dependence of kinetic parameters indicates that at acid pH values (less than or equal to 3.5), the k+2 step is rate limiting in catalysis, whereas for pH values higher than 3.5, k+3 becomes rate limiting. The observed ionizations probably reflect the acid-base equilibria of residues involved in the catalytic diad of papain, His159-Cys25. Comparison with catalytic properties of ficins and bromelains suggests that the results reported here may be of general significance for cysteine proteinase catalyzed reactions.

Binding of the trypsin inhibitor from white mustard (Sinapis alba L.) seeds to bovine beta-trypsin: thermodynamic study

The effect of pH and temperature on the association equilibrium constant (Ka) for the binding of the trypsin inhibitor from white mustard (Sinapis alba L.) seeds (MTI) to bovine beta-trypsin (EC 3.4.21.4) has been investigated. On lowering the pH from 9 to 3, values of Ka for MTI binding to bovine beta-trypsin decrease thus reflecting the acid-pK and -midpoint shifts, upon inhibitor association, of two independent ionizable groups, and of a three-proton transition, respectively. At pH 8.0, values of thermodynamic parameters for MTI binding to bovine beta-trypsin are: Ka = 4.5 X 10(8)M-1, delta G0 = -11.6 kcal/mol, and delta S0 = +53 entropy units (all at 21 degrees C); and delta H0 = +4.1 kcal/mol (temperature independent between 5 degrees C and 45 degrees C). Binding properties of MTI to bovine beta-trypsin have been analyzed in parallel with those concerning macromolecular inhibitor association to serine (pro)enzymes.

Inhibition of serine proteinases by tetra-p-amidinophenoxy-neo-pentane: thermodynamic and molecular modeling study

The inhibitory effect of the aromatic tetra-benzamidine derivative tetra-p-amidinophenoxy-neo-pentane (TAPP) on the catalytic properties of beta-trypsin (EC 3.4.21.4), alpha-thrombin (EC 3.4.21.5), factor Xa (EC 3.4.21.6), Lys77-plasmin (EC 3.4.21.7) and beta-kallikrein-B (EC 3.4.21.35) was investigated (between pH 2 and 8, I = 0.1 M; T = 37 +/- 0.5 degrees C), and analyzed in parallel with that of benzamidine, commonly taken as a molecular inhibitor model of serine proteinases. Over the whole pH range explored, TAPP and benzamidine show the same values of the dissociation inhibition constant (Ki) for beta-trypsin; at variance with the affinity of TAPP for alpha-thrombin, factor Xa, Lys77-plasmin and beta-kallikrein-B which is higher than that found for benzamidine association around neutrality, but tends to converge in the acidic pH limb. On lowering the pH from 5.5 to 3.0, values of Ki for TAPP binding to beta-trypsin as well as for benzamidine association to all the enzymes investigated decreased thus reflecting the pK-shift, upon inhibitor binding, of a single ionizing group. Over the same pH range, values of Ki for TAPP binding to alpha-thrombin, factor Xa, Lys77-plasmin and beta-kallikrein-B may be described as depending on the pK-shift, upon inhibitor association, of two equivalent proton-binding amino acid residues. Considering the X-ray three-dimensional structures and the computer-generated molecular models of serine proteinases: TAPP and :benzamidine adducts, the observed binding behaviour of TAPP and benzamidine to the enzymes considered has been related to the inferred stereochemistry of proteinase: inhibitor contact region(s).

Gabexate mesylate inhibition of serine proteases: thermodynamic and computer-graphics analysis

The inhibitory effect of gabexate mesylate, which is used therapeutically in the treatment of pancreatitis and disseminated intravascular coagulation, and as a regional anticoagulant agent for hemodialysis, has been measured on bovine factor Xa, bovine alpha-thrombin, human Lys77-plasmin, human urinary kallikrein, human urokinase, porcine pancreatic beta-kallikrein-B, and bovine beta-trypsin catalyzed hydrolysis of p-nitrophenyl esters of N-alpha-carbobenzoxy-L-arginine and N-alpha-carbobenzoxy-L-lysine. On the basis of enzyme:gabexate mesylate affinities, the serine proteases can be arranged as follows: human urinary kallikrein approximately porcine pancreatic beta-kallikrein-B much less than bovine beta-trypsin approximately bovine factor Xa approximately human Lys77-plasmin approximately human urokinase approximately bovine alpha-thrombin. The mode of binding of gabexate mesylate to the serine proteases conforms to the active-reactive site geometries observed in their complexes with natural and synthetic inhibitors. Differences in gabexate mesylate affinities for these proteases reflect structural differences at their primary specificity subsite, which have been investigated by comparative analysis of amino acid sequences and by computer-graphics techniques.

Proton NMR and photochemically induced dynamic nuclear polarization studies of peptide fragments obtained by controlled proteolysis of mouse epidermal growth factor

Controlled proteolysis of epidermal growth factor from the mouse leads to fragments of mouse epidermal growth factor containing residues 1-48 and 1-45. The COOH-terminal pentapeptide appears to play a crucial role in determining the hydrophobic interactions between the hormone and the stationary phase during gel chromatography on TSK-125 gel. Proton NMR studies indicate that the overall structure of mouse epidermal growth factor is retained in the protein devoid of the COOH-terminal pentapeptide, while subsequent cleavage of the peptide bond between Arg-45 and Asp-46 starts to perturb the proton resonances most characteristic of the tertiary structure of the hormone, especially those from the aromatic ring protons of Tyr-37. Consequently, photochemically induced dynamic nuclear polarization experiments show an increased exposure of Tyr-37 in the fragment of mouse epidermal growth factor containing residues 1-48. Nuclear Overhauser data suggest that structural changes do occur on fragmentation but seem to be localized in the tiered-beta-sheet domain which contains Tyr-37.

Guanidinophenyl derivatives of pyrazole: synthesis and inhibitory effect on serine proteinases, blood coagulation and platelet aggregation

Guanidinophenyl derivatives of pyrazole have been synthesized. Their inhibitory effects on (i) bovine trypsin, bovine thrombin, porcine pancreatic kallikrein catalyzed hydrolysis of p-nitro anilide of N alpha -benzoyl-arginine and (ii) blood coagulation and platelet aggregation, were investigated. The kinetic behaviour of all compounds conformed to that of a reversible competitive inhibition pattern, and they were also found to act in vitro as inhibitors of platelet aggregation induced by ADP.

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to human Lys77-plasmin

The effect of pH and temperature on the association equilibrium constant (Ka) for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI Kunitz inhibitor) to human Lys77-plasmin has been investigated. Ka values decrease with decreasing pH, reflecting the acid-pK and -midpoint shifts, upon BPTI binding, of a single ionizable group, between pH 5 and 9, and of a three-proton transition, between pH 3 and 5. At pH 8.0, values of thermodynamic parameters for BPTI binding to human Lys77-plasmin are: Ka = 1.2 X 10(9) M-1, delta G degree = -12.2 kcal/mol, and delta S degree = +49 entropy units (at 21 degrees C); and delta H degree = +2.3 kcal/mol (temperature independent between 5 degrees C and 45 degrees C; 1 kcal = 4184 J). BPTI binding properties of human Lys77-plasmin have been analysed in parallel with those of serine (pro)enzymes acting on cationic and non-cationic substrates. Considering the known molecular structures of homologous serine (pro)enzymes, or Kunitz and Kazal-type inhibitors and of their complexes, the observed binding behaviour of BPTI to human Lys77-plasmin was related to the inferred stereochemistry of the enzyme-inhibitor contact region.

Catalytic properties of bovine alpha-thrombin: a comparative steady-state and pre-steady-state study

Values of steady-state and pre-steady-state parameters for the bovine alpha-thrombin-catalyzed hydrolysis of ZArgONp and ZLysONp have been determined between pH 2.5 and 8 (I = 0.1 M) at 21 +/- 0.5 degree C. Kinetic properties of bovine alpha-thrombin have been analyzed in parallel with those of porcine pancreatic beta-kallikrein-B and bovine beta-trypsin, all acting on cationic substrates. The different primary specificity and catalytic behaviour of these three serine proteinases reflect subtle structural differences at their S1 subsite, especially at residue positions 190, 221 and 226 as well as in the 217-219 segment.

Primary specificity of ancrod, the coagulating serine proteinase from the Malayan pit viper (Agkistrodon rhodostoma) venom

Values of steady-state and pre-steady-state parameters for the hydrolysis of ZArgONp and ZLysONp catalysed by ancrod, the coagulating serine proteinase from the Malayan pit viper (Agkistrodon rhodostoma) venom, have been determined, between pH 2.5 and 8 (I = 0.1 M) at 21 +/- 0.5 degrees C, and analysed in parallel with those of bovine alpha-thrombin and porcine pancreatic beta-kallikrein-B. In addition to the well-known coagulating behaviour, ancrod also shows catalytic properties, in the hydrolysis of ZArgONp and ZLysONp, reminiscent of those of porcine pancreatic beta-kallikrein-B.

1H-NMR of reverse micelles. II: Conformational studies of peptides and proteins in the AOT/water/isooctane system

The interaction of AOT reverse micelles with Met-enkephalin, the pancreatic secretory trypsin inhibitor (PSTI) and the epidermal growth factor (EGF) is examined by NMR methods and the three systems are compared. While Met-enkephalin adopts a folded conformation, PSTI appears to become highly flexible, suggestive of a non-specific interaction with the micelles. On the other hand, the EGF spectrum shows that, although the main globular features of the protein are retained in the presence of AOT, the C-terminal fragment has to rearrange its conformation when put in contact with the micelle wall.

Aromatic tetra-amidines: antiproteolytic and antiesterolytic activities towards serine proteinases involved in blood coagulation and clot lysis

The inhibitory effect of 1,3-di-(p-amidinophenoxy)-2,2-bis-(p-amidinophenoxymethyl)propane (TAPP-H), TAPP-halo derivatives (with Cl, Br or I) and benzamidine on the Ancrod, bovine Factor Xa, and human plasmin catalyzed hydrolysis of esters and anilides of amino acids was investigated, at pH 8.1 and 37 degrees, and compared with that shown from these compounds on bovine thrombin and porcine pancreatic kallikrein catalysis. The inhibitory effect of TAPP-H and TAPP-halo derivatives on the proteinases considered, involved, to different extents, in blood coagulation and clot lysis, is higher by at least 10-fold, than that of benzamidine, which binds at the primary specificity subsite (S1) of serine endopeptidases and is commonly taken as a molecular inhibitor model. The high inhibitory effect of aromatic tetra-amidines has been interpreted taking into account an additional productive binding for a second benzamidine or halo-benzamidine moiety to the enzyme surface. Moreover, the data reported here allowed us to clarify the inhibition mechanism (in vitro) of TAPP-H on blood coagulation, induced by the "cancer coagulation factor" produced by the Walker carcinoma in Wistar rats and on the fibrinogen-to-fibrin conversion, and to identify some serine proteinases which act as targets for aromatic tetra-amidines.

1H-NMR of reverse micelles. I: The surfactant resonances as probes for the AOT/water/isooctane system

1H-NMR spectra of Aerosol-OT (AOT) reverse micelles in isooctane are reported at various water contents and several temperatures. The resonances from the AOT protons near the polar head are completely assigned. The NMR parameters (chemical shift and linewidth) appear to be suitable probes for characterizing the physico-chemical state of micelles, in particular in order to define the range in which the system is fully homogeneous and transparent. The results correlate well with those obtained from optical density measurements. Lanthanide ions dissolved in the water phase selectively perturb the AOT resonances from the protons nearest to the polar head; conversely, non-polar shift reagents soluble in the organic phase do not cause appreciable effects on any of the observable signals.

Trypsin activation. Effect of the Ile-Val dipeptide concentration on Kazal inhibitor binding to bovine trypsinogen

The effect of Ile-Val concentration (up to 2.0 M) on the thermodynamic parameters for the binding of the porcine pancreatic secretory trypsin inhibitor (Kazal inhibitor) to trypsinogen has been investigated at pH 5.5 between 7 degrees C and 42 degrees C. Thermodynamic parameters for Kazal inhibitor binding to the Ile-Val:zymogen adduct are more favorable than those observed for inhibitor association to the free proenzyme, but less so than those reported for beta-trypsin:Kazal inhibitor adduct formation (even under saturating dipeptide concentrations), suggesting that the effector dipeptide does not induce a complete rigidification of the proenzyme's activation domain. Considering the dependence of the association equilibrium constant for Kazal inhibitor binding to trypsinogen from Ile-Val concentration, thermodynamic parameters for the effector dipeptide binding to the free proenzyme and to its binary complex with Kazal inhibitor have been obtained. Differences in affinity for Ile-Val binding to the free zymogen and its binary complexes with inhibitors and substrates are indicative of the presence of different activation levels of the proenzyme, none of them exactly coincident with that of beta-trypsin. Such different discrete states should correspond to those involved in the zymogen-to-active-enzyme transition which should not be considered as an all-or-nothing process, but as a multistep event.