Interaction of manganese with bovine factor X

Factor VIII assay mimicking in vivo coagulation conditions

Under certain circumstances, the determination of coagulation factor VIII (FVIII) is hampered by assay discrepancies between clotting and chromogenic approaches. These are observed in certain patients' plasma as well as in certain concentrates. We intended to develop a novel assay for the quantification of coagulation FVIII which reflects the physiological situation better than the established assays. It is based on plasma without chelation of divalent cations and simultaneously minimizes the generation of activated factors which could function as uncontrolled triggers of coagulation. FVIII deficient plasma is prepared with the aid of biotinylated antibodies against FVIII from normal plasma in presence of inhibitors of contact activation. To start the assay only tiny amounts of activated FIX serve as trigger. The FVIII determination is performed in a kinetic experiment and is based on the cleavage of a fluorogenic substrate for activated FX. FVIII concentrations between 0.01 and 1 IU mL(-1) are easily determined. Plasma-derived and recombinant FVIII concentrates were compared. All plasma-derived concentrates were found to contain FVIII activities within the specification of the manufacturer. Recombinant concentrates yielded only 35-50% of the claimed potency. The novel in vivo-like assay avoids the undue advantage or disadvantage of certain product characteristics by eliminating unphysiological assay conditions. Its usefulness could turn out in future experiments with plasma from haemophilia A patients.

Properties of recombinant chimeric human protein C and activated protein C containing the gamma-carboxyglutamic acid and trailing helical stack domains of protein C replaced by those of human coagulation factor IX

The properties of a recombinant (r) chimeric human protein C (PC) containing replacement of its gamma-carboxyglutamic acid (Gla) and helical stack (HS) domains by those of human coagulation factor IX (fIX) have been examined. Titration with Ca2+ of the divalent cation-induced intrinsic fluorescence quenching of this chimera (r-GDIX/PC) allowed determination of the [Ca2+], of 1.8 mM, required to produce this alteration in 50% of the protein molecules. These values were 0.41 and 0.61 mM for wtr-PC and fIX, respectively. The chimera did not react with a Ca(2+)-dependent, Gla domain-directed conformational monoclonal antibody (MAb) to r-PC but did interact with a similar MAb (H5B7) to fIX. The [Ca2+] required to induced H5B7 binding to 50% of the r-GDIX/PC molecules was 6.6 mM, while this same value for fIX was a nearly identical 7.2 mM. The [Ca2+] needed for binding of 50% of r-GDIX/PC to acidic phospholipid (PL) vesicles was 0.58 mM, while that for wtr-PC and fIX were 1.2 and 0.55 mM, respectively. The [protein] required for 50% binding of r-GDIX/PC to PL at 20 mM Ca2+ was 0.29 microM. These same values for r-PC and fIX were 0.38 and 1.8 microM, respectively. The Ca(2+)-mediated inhibition of the thrombin-catalyzed activation of r-GDIX/PC was characterized by a Ki of 118 microM, a value similar to that of 125 microM obtained for this same inhibition of wtr-PC activation. The thrombin-catalyzed activation of both r-GDIX/PC and wtr-PC was stimulated by soluble r-thrombomodulin. Similar to the case of wtr-PC, Ca2+ initially enhanced and, at higher concentrations, inhibited the activation of r-GDIX/PC. The Km and kcat values for this latter activation at optimal [Ca2+] (100 microM) were 4.1 microM and 2.5 s-1, respectively. These same kinetic constants for activation of wtr-PC were 4.3 microM and 2.9 s-1, respectively. These results show that many of the features needed for functional integrity of the Ca2+-bound Gla/HS domains of PC are also present in those same modules of fIX, a finding that points to a generalized functional role for the Ca2+-induced conformation of the structural unit consisting of the Gla and HS domains. The data also suggest that the Ca2+-bound form of the Gla/HS region is an independently folded unit in PC and perhaps in fIX.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding of calcium to synthetic peptides containing gamma-carboxyglutamic acid

The Ca2+ binding properties of various gamma-carboxyglutamic acid (gla)-containing synthetic peptides with counterpart sequences in human protein C were investigated employing potentiometry with a Ca(2+)-selective electrode and titration calorimetric techniques. The shortest peptides, FL(gla)(gla)LR, DF(gla)(gla)AK, and the oxidized form of the cyclic hexapeptide CI(gla)(gla)IC, each of which contains one pair of gla residues, have a weak affinity for Ca2+, with some peptides probably involved in intermolecular bridging of the Ca2+. The best example of this is the oxidized form of the peptide, CI(gla)(gla)IC, where one g-atom of Ca2+ interacts with 2 mol of peptide (n = 0.5) with a Kd value of 1.6 mM. A second g-atom of Ca2+ interacts with 2 mol of this same peptide (n = 0.5) and is characterized by a Kd of 8.8 mM. A longer peptide containing this same sequence, viz. L(gla)R(gla)CI(gla)(gla)IC, possesses two binding sites (n = 2.0) for Ca2+ of Kd = 16.1 mM, as well as a tighter site (n = 1), of Kd = 0.4 mM. An increase in stoichiometry of tight binding sites as the peptide is elongated is observed from binding data obtained on a 38-residue peptide that possesses all nine of the gla-residues of protein C in their proper sequence positions. The strongest Ca2+ binding sites (n = 3-4) possess an average Kd of 0.4 mM, followed by another class of sites (n = 5-10, average Kd = 1.5-3.0 mM). The affinity and stoichiometry of these stronger sites mimic those observed for binding of Ca2+ to the gla region of prothrombin fragment 1.(ABSTRACT TRUNCATED AT 250 WORDS)

The kinetic assembly of the intrinsic bovine factor X activation system

The activation of bovine factor X by bovine factors IXa alpha and IXa beta has been examined under conditions of progressive assembly of the complete intrinsic activation system, i.e., factor X/factor IXa/Ca2+/phospholipid (PL)/factor VIIIa. In the presence of Ca2+, and the absence of PL and factor VIIIa, factor IXa alpha is a more efficient enzyme than factor IXa beta toward factor X activation, primarily due to the much higher kcat for the factor IXa alpha-catalyzed reaction. Analysis of the steady-state kinetic properties, after addition of PL (mixtures of phosphatidylcholine/phosphatidylserine) to the factor X/factor IXa/Ca2+ activation system, shows that the mechanism most closely follows a nonessential activation scheme, where the true substrate is the factor X/Ca2+/PL complex. The presence of PL results in a large (1-2 orders of magnitude) increase of the kcat for factor IXa beta, but does not substantially affect the steady-state kinetic constants of the factor IXa alpha-catalyzed reaction. Examination of the steady-state activation kinetics of factor X, after addition of factor VIIIa to factor X/factor IXa/Ca2+/PL, demonstrates that the mechanism is most consistent with a nonessential activation scheme of fluid phase substrate (factor X) being activated by a PL-bound enzyme system (factor IXa/Ca2+/factor VIIIa/PL). The presence of factor VIIIa stimulated the rates of factor X activation by factor IXa beta/Ca2+/PL by 1-2 orders of magnitude. Qualitatively similar behavior was noted for the factor IXa alpha-catalyzed activation. The results of this manuscript show that, in the presence of Ca2+ and absence of other cofactors, factor IXa alpha is a much more efficient enzyme for factor X activation, as compared to factor IXa beta. This is likely due to effects on the system resulting from covalent retention of the negatively charged activation peptide, by factor IXa alpha. However, the enzymatic activity of factor IXa beta shows a far better response to cofactors, particularly PL, than factor IXa alpha, thereby rendering factor IXa beta the more efficient enzyme in the complete intrinsic activation system.

The binding of Mn2+ to bovine plasma protein C, des(1-41)-light chain protein C, and activated des(1-41)-light chain activated protein C

The binding isotherms of Mn2+ to bovine plasma protein C (PC), des(1-41)-light chain protein C (GDPC), and activated GDPC (GDAPC) have been measured. PC contains 14-16 total Mn2+ binding sites, a value that is reduced to approximately 7-8 in the presence of NaCl. The average Kd of the latter sites is 230 +/- 30 microM. Upon removal of a 41-residue peptide from the amino terminus of the light chain of PC, and, concomitantly, all of the gamma-carboxyglutamic acid residues, the resulting protein, GDPC, possesses a single Mn2+ site of Kd = 120 +/- 20 microM. Activation of GDPC to GDAPC results in a slight lowering of the Kd for the single Mn2+ binding site to 53 +/- 8 microM, a value that is essentially unchanged in the presence of monovalent cations, a competitive inhibitor of the enzyme, or an active site directed affinity label. The Mn2+ on GDAPC is displaced by Ca2+, suggesting that the protein binding site for these two divalent cations is the same. These studies establish that Mn2+ is a suitable spectroscopic probe for the Ca2+ binding site of GDAPC, and that the divalent cation site is separate from the monovalent cation site(s) and the active site of the enzyme.

The effect of calcium on the thermotropic properties of bovine blood coagulation factors IX and X and their activation intermediates and products

The thermotropic properties of bovine blood coagulation Factors IX and X, as well as the activation intermediates and products of these proteins, have been investigated by differential scanning microcalorimetry in the presence and absence of Ca2+. Bovine Factor IX displays a single thermal-denaturation transition characterized by a temperature midpoint (TM) of 54.5 +/- 0.5 degrees C and a calorimetric enthalpy (delta Hc) of 105 +/- 15 kcal/mol, in the absence of Ca2+. In the presence of Ca2+ concentrations sufficient to saturate its sites on Factor IX, the Tm value is increased to 57.0 +/- 0.5 degrees C and the delta Hc is virtually unchanged. When the activation intermediate, Factor IX alpha, is similarly analyzed in the absence of Ca2+, a broad, diffuse thermogram was obtained which did not lend itself to calculation of thermodynamic parameters. In the presence of Ca2+, Factor IX alpha displayed thermograms characterized by a TM of 51.0 +/- 0.5 degrees C and a delta Hc of 109 +/- 10 kcal/mol. The activated product, Factor IXa alpha, in the absence of Ca2+ (the values in the presence of saturating Ca2+ are given in parentheses), undergoes thermal denaturation with a TM of 54.5 +/- 0.5 degrees C (57.0 +/- 0.5 degrees C) and a delta Hc of 158 +/- 10 kcal/mol (156 +/- 10 kcal/mol). Similarly, the terminal-activation product, Factor IXa beta, displays a TM of 51.5 +/- 0.5 degrees C (54.0 +/- 0.5 degrees C) and a delta Hc of 85 +/- 5 kcal/mol (126 +/- 10 kcal/mol). Bovine blood coagulation Factor X has been analyzed in this same fashion, and shows very similar thermal properties to Factor IX. The thermal denaturation of Factor X is represented by a TM of 54.0 +/- 0.5 degrees C (55.0 +/- 0.5 degrees C) and a delta Hc of 102 +/- 10 kcal/mol (118 +/- 10 kcal/mol), whereas its activated form, Factor Xa beta, possesses a TM of 55.0 +/- 0.5 degrees C (55.0 +/- 0.5 degrees C) and a delta Hc of 92.0 +/- 5 kcal/mol (136 +/- 10 kcal/mol). These studies indicate that, for many of these proteins, Ca2+ induces a conformational alteration to a more thermally stable form, which also requires the absorption of greater amounts of heat for thermal denaturation.

Cation binding properties of the multiple subforms of RVV-X, the coagulant protein from Vipera russelli

The factor X activating enzyme from Russell's viper venom (RVV-X) has been shown to exist in multiple subforms, distinguished from each other by their isoelectric points. The differences in isoelectric points were due, as least in part, to dissimilarities in the respective sialic acid contents of the subforms. No functional difference was, however, discovered between any of the subforms. All of the subforms were found, by equilibrium ultrafiltration, to bind Ca2+ reversibly. At least two equivalent Ca2+ binding sites were observed on each protein molecule (Mr 79 000), with a KD of 50 +/- 15 microM at pH 7.4 and 25 degrees C. A new substrate for RVV-X, which does not bind Ca2+, apoprotein AI from human high-density lipoprotein, was used to show that this reversibly bound Ca2+ was not essential for enzymic activity. All subforms have also been shown, by atomic absorption analysis, to contain nonexchangeable metal ions, to the extent of 1 mol of Ca2+ and 0.7 mol of Zn2+ per mol of protein. No Mn2+ or Mg2+ was detected. This nonexchangeable Ca2+ and Zn2+ could only be removed from the protein by incubation at pH 3.0 or by treatment with 6 M guanidine hydrochloride, conditions under which the protein lost activity irreversibly.

A simplified procedure for purification of human prothrombin, factor IX and factor X

A simplified procedure is described for the purification of prothrombin, Factor X and Factor IX in overall yields of 35-40% from pooled human plasma. The initial steps, which are common to prior purification techniques, include adsorption onto and elution from barium citrate, ammonium sulfate fractionation, and DEAE-Sephadex chromatography. The procedure differs from previous techniques in that the nest step, heparin-agarose chromatography, is carried out in a (sodium) citrate buffer, pH 7.5. These chromatographic conditions permit the separation of prothrombin, Factor X and Factor IX from each other, yielding fractions with apparent homogeneity in several electrophoretic systems. The additional chromatographic steps of earlier purification procedures are therefore unnecessary. The heaprin-agrarose column chromatographic conditions consistently resulted in the separation of human prothrombin in into two fractions in a ratio of approximately 4:1. Both fractions possess similar specific activity in a one stage prothrombin assay, and also activate at the same rate in a Factor Xa, Ca2+ and phospholipid system. Both fractions of prothrombin also comigrate in sodium dodecyl sulfate gel electrophoresis with an apparent Mr integral of 70,000.

Zymogens and cofactors of blood coagulation

Blood coagulation is a system in which a series of zymogens of serine proteases are sequentially activated. In this regard, there is little fundamental difference between coagulation and the activation of the homologous pancreatic zymogens. There are, however, several aspects unique to coagulation which are discussed in detail. These are (1) the requirement for a high-molecular-weight protein or lipoprotein cofactor for optimal reaction rates, (2) the requirement for membranes or a membrane-like surface which further distinguishes this system; (3) a metal ion requirement for most reactions (in contrast to the pancreatic serine proteases) relating to the content of the newly described amino acid gamma-carboxyglutamic acid in the four vitamin K-dependent proteins, regarding which recent data relating to the metal binding sites on prothrombin are discussed in detail; and (4) the uniqueness of the initiating reactions in comparison to those which activate the pancreatic zymogens, insofar as no enzyme corresponding to enterokinase has been identified. The implications of this phenomenon are analyzed with particular attention to the potential role of the endogenous activity of certain zymogens in initiating coagulation. The article deals finally with the specific problems attendant on analyzing a system in which many serine proteases lacking absolute specificity are generated and regulated.