Phospholipid-binding properties of bovine factor V and factor Va

Factor V and factor Va binding to single bilayer phospholipid vesicles was investigated by light-scattering intensity measurements. This technique allows the measurement of free and phospholipid-bound protein concentrations from which equilibrium constants can be obtained. As controls, the Ca2+-dependent phospholipid binding of prothrombin and factor X were also studied. The average values obtained for the dissociation constants (Kd) and lipid to protein ratio at saturation, moles/mole (n), for prothrombin (Kd = 2.3 X 10(-6) M, n = 104) and factor X (Kd = 2.5 X 10(-6) M, n = 46) binding to vesicles containing 25% Folch fraction III and 75% phosphatidylcholine in the presence of 2 mM Ca2+ were in agreement with those reported in the literature. The average factor V and factor Va values for the dissociation constants and lipid to protein ratio at saturation (moles/mole) were Kd = 7.2 X 10(-8) M and n = 270 for factor V and Kd = 4.4 X 10(-7) M and n = 76 for factor Va. In contrast to prothrombin and factor X, factor V and factor Va demonstrated Ca2+-independent lipid binding. In addition, the number of factor V and factor Va molecules bound per vesicle was found to be dependent both on the phosphatidylserine content of the vesicle and the ionic strength of the buffer.

The covalent differences between bovine alpha- and beta-thrombin. A structural explanation for the changes in catalytic activity

The partial covalent structure of bovine beta-thrombin has been determined by the use of automated Edman degradation and carboxypeptidase digestion of the component polypeptide chains separated by gel filtration following either reduction and carboxymethylation or performic acid oxidation. beta-Thrombin has been found to contain three peptide chains derived by proteolysis of the parent alpha-thrombin molecule. The A chain of alpha-thrombin has been cleaved at two points yielding a peptide (A1 chain) which contains 17 amino acids, beginning with threonine 14 and ending with lysine 30. The B chain of alpha-thrombin has been cleaved at two positions to yield a B1 chain which begins with the NH2-terminal isoleucine and terminates with lysine 65 and a B2 chain which begins with lysine 74 and continues through COOH-terminal serine 259. The A1 chain and B2 chain are linked by a disulfide bridge. Although there is no evidence for a covalent bond between the B1 chain and the B2-A1 chains, the B1 chain is tightly bound to the remainder of the molecule, for separation is achieved only under denaturing conditions.

The turnover in normal dogs of prothrombin and its fragments; effect of induced intravascular coagulation

When 125I-labeled canine prothrombin was given to normal adult dogs intravenously, it was calculated that 240% of the plasma prothrombin crossed the capillary barrier per day, 410% of the interstitial prothrombin returned to the blood stream daily, and 79% of the plasmatic prothrombin was catabolized per day. These data are in close agreement with those observed for bovine prothrombin in calves by Takeda (1970). When derived from normal dog prothrombin, prethrombin-1 is a mixture of 2 polypeptides, one larger than the other, and both present in about equal amounts. The longer peptide, "prethrombin-1-long," was catabolized twice as fast as prothrombin, and the shorter, "prethrombin-1-short," 4 times faster. Prothrombin fragment-1 was catabolized by the normal dog still more rapidly. The catabolism of prothrombin was not accelerated in 3 dogs receiving continuous infusions of a thromboplastic emulsion of dog brain. Nor was the level of prothrombin in their plasma remarkably altered.

Isolation of human platelet and red blood cell plasma membrane proteins by preparative detergent electrophoresis

High resolution polyacrylamide gel electrophoretic techniques have been applied to the preparative isolation and analysis of plasma membrane proteins and glycoproteins from human platelets and red blood cells. The techniques presented allow relatively simple, direct, rapid and quantitative purification of a broad molecular weight range of membrane proteins, by means of continuous elution preparative gel electrophoresis of protein solubilized with sodium dodecyl sulfate. Spectrophotometric and fluorophotometric (fluorescamine) profiling, and high resolution gel electrophoretic analysis (SDS-acrylamide gradient slab gels, and gel electrofocusing) of eluted protein species indicate that purified membrane proteins of a broad molecular weight range may be obtained in a one step procedure, and in quantities and concentrations sufficient for further analytical or experimental procedures.

Prothrombin domains: circular dichroic evidence for a lack of cooperativity

The far-ultraviolet circular dichroism spectra of bovine and human prothrombin, prothrombin fragment 1, prethrombin 1, prothrombin fragment 2, and prethrombin 2 (prethrombin 2des(1--13)) were determined and the method of Chen et al. [Chen, Y. H., Yang, J. T., & Martinez, H. M. (1972) Biochemistry 11, 4120--4131; Chen, Y. H., Yang, J. T., & Chau, K. H. (1974) Biochemistry 13, 3350--3359] was used to calculate the apparent alpha-helix, beta-sheet, and random-coil contents of each protein. Prothrombin and its activation components were found to contain a large amount of aperiodic secondary structure and there was little species difference between the spectra and, thus, secondary structures. The hypothesis that the prothrombin activation components exist as relative ly noncooperative "domains" within the prothrombin molecule was tested by comparing the circular dichroism spectrum of prothrombin with the sum of the spectra of the components. It support of the hypothesis, no gross alterations in the spectra and, hence, secondary structures of the components were found to have occurred upon activation.

Ultrastructural characteristics of dog and human platelets adherent to native and collagen-coupled cuprophan

Adhesion of human and dog platelets to native and collagen-coupled Cuprophan under defined flow conditions was studied by scanning and transmission electron microscopy. Dog platelets, singly adherent to and uniformly distributed on both native and collagen-coupled Cuprophan, extend slender pseudopods across the surface without evidence of degranulation. Human platelets, while not adhering to native Cuprophan, formed irregularly shaped, semi-confluent cytoplasmic sheets on the collagen-coupled surface. Extensive cytoplasmic reorganization and degranulation suggests a post-release state of the human platelets. Aspirin had no apparent effect on either human or dog platelet adhesion or upon the apparent release state of the human platelets.

Thrombin-catalyzed activation of single chain bovine factor V

The thrombin-catalyzed activation of single chain bovine Factor V was found to proceed by cleavage of the parent molecule (Mr = 330,000) to intermediates of apparent Mr = 205,000 and 150,000 followed by cleavage of the latter to end products of 94,000 and 74,000 apparent molecular weights. The generation of Factor Va activity coincides with the second cleavage. Further cleavages of the Mr = 205,000 component to apparent Mr = 74,000 and 32,000 fragments and possibly to others also occurred at a slower rate with little or no further increase in activity. The nature of the products and intermediates was unchanged regardless of whether the activation process was complete in either 1 or 10 min. Factor Xa did not catalyze the cleavage nor enhance the activity of Factor V under conditions in which the activation by comparable amounts of thrombin was complete. It was shown using either discrete clotting assays or continuous thrombin analysis with a chromogenic substrate that Factor V was subject to activation in situ by newly formed thrombin in a system initially containing prothrombin, Factor Xa, Ca2+, phospholipid, and unactivated Factor V. The rate of activation of prethrombin 1 was found to be saturable with added Factor Va when all other components were present at fixed levels. The amount of Factor Va required to achieve saturation was linearly dependent on the amount of Factor Xa present, indicating that the two factors interact stoichiometrically in the "prothrombinase" complex.

Isolation and characterization of single chain bovine factor V

A procedure for the isolation of bovine Factor V has been developed. The Factor V is isolated from bovine plasma by a series of steps including barium citrate adsorption, polyethylene glycol precipitation, QAE-cellulose adsorption, hydrophobic chromatography on octyl Sepharose, ammonium sulfate fractionation, preparative electrophoresis on acrylamide gels, and finally, phenyl Sepharose chromatography. During isolation, judicious use of inhibitors including benzamidine hydrochloride, soybean trypsin inhibitor, and diisopropylphosphorofluoridate has been applied to prevent activation of the Factor V TO Factor Va. The activity of the isolated protein increases by a factor of 80 when stimulated by catalytic amounts of thrombin. The specific activity of the material after thrombin activation is 1250 units/mg of protein when evaluated versus a bovine Factor V standard in human factor V-deficient plasma. The isolated protein is a single component when analyzed by a variety of electrophoretic techniques and has been characterized in terms of its gross physical and chemical properties. Bovine Factor V is a single chain glycoprotein which has a molecular weight of 330,000. The single chain nature of the molecule has been established by sedimentation equilibrium studies of the native molecule and on the molecule in 6 M guanidinium chloride with and without disulfide bond reduction. In addition to these mass measurements, the single chain nature of the molecule has been established by hydrodynamic estimation of the random coil volume by sedimentation velocity studies of the reduced carboxyamidomethylated protein in 6 M guanidinium chloride. Native Factor V has a sedimentation coefficient so20,w of 9.19 S, which indicates the molecule is highly asymmetric. The frictional ratio f/fmin for the molecule is estimated to be 2.01, and the axial ratio of the equivalent prolate ellipsoid is 25:1. Thus, present data suggest that Factor V is a rod-like molecule composed of a single chain.

Metal ion induced conformational transitions of prothrombin and prothrombin fragment 1

Circular dichroism experiments indicate that prothrombin fragment 1 undergoes essentially the same secondary structural change whether in the presence of Ca(2+), Mg(2+), or Mn(2+). Titration with any of these metal ions results in a sigmoidal titration curve indicative of cooperative binding. Mg(2+) and Ca(2+) have nearly identical transition midpoints, while that for Mn(2+) is an order of magnitude less. These results correlate well with the results of previous metal ion intrinsic fluorescence quenching experiments. Fragment 1 has previously been shown to undergo a second transition corresponding to dimerization at high calcium concentrations. The present circular dichroism experiments show that this transition does not result in a gross alteration of secondary structure in the fragment 1 molecule. Studies with prothrombin, similar to those with fragment 1, indicate a similar metal ion dependent conformational change but of smaller magnitude. As apparently only the fragment 1 portion of the molecule undergoes the transition, it would appear that the covalently linked fragment 1 is constrained from attaining the same conformation as the purified entity. This suggests that caution must be used in interpreting the results of metal ion binding studies using fragment 1 as an analogue for prothrombin.

Comparison of the inhibition of thrombin by three plasma protease inhibitors

Human alpha-thrombin is inhibited by the circulating protease inhibitors alpha1-antitrypsin, antithrombin III, and alpha2-macroglobulin. Kinetic analyses of the inhibitor thrombin interactions were carried out utilizing either fibrinogen or the synthetic substrate Bz-Phe-Val-Arg-p-nitroanilide as substrates to determine residual thrombin activity. These studies demonstrated that the inhibition of thrombin by alpha1-antitrypsin, antithrombin III, and alpha2-macroglobulin followed second-order kinetics. The rate constants for the inhibition of thrombin by alpha1-antitrypsin, antithrombin III, and alpha2-macroglobulin are 6.51 +/- 0.38 x 10(3), 3.36 +/- 0.34 x 10(5), and 2.93 +/- 0.02 x 10(4) M-1 min-1, respectively. Comparison of the second-order rate constants and the normal plasma levels of the three inhibitors demonstrates that, under the in vitro conditions utilized, antithrombin III is five times and alpha2-macroglobulin is one-third as effective as alpha1-antitrypsin in the inhibition of thrombin.

Prothrombin Quick. A newly identified dysprothrombinemia

The rarest of reported inherited plasmatic coagulopathies involve prothrombin. Only 10 families with significant reductions of this plasma protein (hypoprothrombinemia) have been observed. Even fewer, six families, have been found to have a functionally abnormal prothrombin (dysprothrombinemia) in their blood. An as yet undefined prothrombin abnormally has been recognized in eight other families. One of the first patients previously identified by Quick and his associates as having a defect in her plasma prothrombin has been shown to have about half the normal amount of prothrombin antigen but virtually no prothrombic function. We propose that this dysprothrombin be designated prothrombin Quick. An additional patient also first described by Quick was found to be truly hypoprothrombinemic--that is, to lack both functional and antigenic prothrombin. Briefly summarized are the other five families with dysprothrombinemia, nine with hypoprothrombinemia, and the eight in whom the defect has not been classified.

Cultured aortic endothelial cells from pigs with von Willebrand disease: in vitro model for studying the molecular defect(s) of the disease

Aortic endothelial cells from normal pigs and pigs with von Willebrand disease have been established in long-term cultures. Both cultures appeared similar in terms of general growth characteristics, morphologic features and ultrastructure. Immunofluorescent staining of these cultures with chicken (or rabbit) antiporcine ristocetin-Willebrand factor sera (or IgG) resulted in extensive perinuclear staining of the cells in both cultures. Additionally, staining of semiconfluent cultures of normal cells for ristocetin-Willebrand factor revealed an extensive meshwork of distinct, immunologically identifiable ristocetin-Willebrand factor-containing filaments between cells. Immunoreactive material was considerably decreased and more diffuse between cells in semiconfluent cultures from affected pigs. Through immunocytochemical staining with peroxidase-coupled antiserum, the filaments (of indeterminate length) were found to have a diameter of approximately 300 A. Finally, washed porcine platelets interacted extensively with scrape-damaged cultures of affected endothelial cells. This interaction of platelets with damaged normal cultures was abolished by pretreatment of the cultures with rabbit antiporcine ristocetin-Willebrand factor IgG.

Purification of porcine and human ristocetin-Willebrand factor

A plasmatic component required for the ristocetin-induced aggregation of platelets has been purified from normal human and porcine plasma by gel filtration (4% agarose) and anion-exchange chromatography (DEAE cellulose). No factor VIII coagulant activity was found associated with the purified human or porcine component. Urea sodium dodecylsulfate electrophoretic analysis of the purified component of both species indicated that the apparent molecular weight with intact disulfides is in excess of 500,000; after disulfide reduction with 2-mercaptoethanol, single components with an apparent subunit molecular weight of 230,000 were observed. Purified porcine ristocetin-Willebrand factor (RWF) co-sedimented in sucrose gradients with the factor present in normal plasma. Amino acid analysis of both human and porcine RWF indicated that all normal amino acids are present, whereas amino sugars were undetected. However, lipid analysis indicated 1% to 2% lipids present, including monoglycerides, di- and tri-glycerides, cholesterol, cholesterol esters, some free fatty acids, and a trace of phospholipid. A single line of identity was observed between normal human plasma and purified human RWF when immunodiffusion plates were run with purified rabbit anti-human RWF immunoglobulins. Antisera raised against human and porcine RWF's do not inhibit the factor VIII coagulant activity of the homologous plasma, nor is "spontaneously occurring" human factor VIII inhibitor neutralized by the isolated material of either species.

Differentiation of metal ion-induced transitions of prothrombin fragment 1

The intrinsic fluorescence of human and bovine prothrombin fragment 1 is quenched (approximately -35%) when calcium ions are bound. The intrinsic fluorescence of prothrombin is also quenched by the binding of Ca2+ but to a lesser extent (total change is approximately -6%). The prothrombin fragment 1 fluorescence transition is also effected by the binding of Mg2+, Mn2+, Gd3+, and Tb3+. With all ions the fluorescence quenching is readily reversed by titration with EDTA. Titration with any of the above ions results in a sigmoidal titration curve. The fluorescence transition midpoints (expressed as Tm) occur at the following concentrations of ions: Ca2+, 0.22 (0.35) mM; Mg2+, 0.22 (0.45) mM; Mn2+, 12.6 (12.6) muM; and Gd3+, 3.6 (5.3) muM (the values in parentheses indicate the concentration of the respective ions bound to bovine prothrombin fragment 1). The presence of phospholipid steepens the Ca2+ titration curve, significantly more so for the bovine system than for the human. Tm values for Ca2+ binding in the presence of phospholipid are 0.21 mM and 0.22 mM for binding to human and bovine prothrombin fragment 1, respectively. Sedimentation equilibrium and velocity studies indicate that prothrombin fragment 1 which is monomeric in the presence of EDTA undergoes concentration-dependent association in the presence of Ca2+. A plot of fraction monomer versus Ca2+ concentration is sigmoidal, with a Tm of approximately 1 mM Ca2+. Mg2+ is only marginally effective in promoting the dimerization, and Mn2+ and Gd3+ are even less effective. However, sedimentation studies performed in the presence of 1 mM Mg2+ at varying Ca2+ concentrations shifted the apparent dimerization transition markedly to the left, the midpoint of the transition occurring at 0.25 mM. Kinetic studies reveal that while Mg2+ by itself does not promote prothrombin activation to thrombin, Mg2+ will partially substitute for Ca2+ in prothrombin activation. In the presence of 1 mM Mg2+ maximal activation rates are attained with 0.3 mM Ca2+; higher Mg2+ concentrations (at this Ca2+ concentration) are inhibitory. Only Ca2+ and Gd3+ permit significant prothrombin-phospholipid binding. Scatchard plots derived from equilibrium dialysis experiments performed with bovine prothrombin fragment 1 suggest marked cooperativity in calcium binding and the existence of approximately six Ca2+ binding sites. Similar studies, but with 1 mM Mg2+ also present in the dialysate, suggested that Mg2+ promotes a greater degree of cooperativity in Ca2+ binding to prothrombin fragment 1 with an apparent decrease in the number of Ca2+ sites occupied. It therefore appears that prothrombin fragment 1 has two classes of metal ion binding sites. One class, probably comprising two of six sites, is apparently fairly nonselective with respect to which metal ion is bound; binding of metal ion to these sites is responsible for the fluorescence change and apparently triggers a conformational transition...

Ultrastructural cytochemistry of platelets and megakaryocytes in the carcinoid syndrome

Platelets and megakaryocytes from 11 patients with the carcinoid syndrome have been studied by transmission electron microscopy. Cells fixed in phosphate-buffered glutaraldehyde are oval to discoid, with pseudopods, a dilated open-channel system, and a prominent dense tubular system as defined by peroxidase activity and alkaline bismuth stain. Atypical with hexagonal lattices and treaded substructures and large (diameter greater than 0.5 mum), phosphatase-positive, debris-containing vacuoles are four times more numerous than in normal platelets. Incubation of platelets in a 0.05% suspension of latex results in particle incorporation into phagosomes and the debris-containing vacuoles. Molybdate-dichromate stain reveals two classes of dense bodies, one of which (with a reticular core) is 20 times more numerous than in normal platelets. Bone marrow megakaryocytes lack both dense bodies and debris vacuoles analogous to those found in circulating platelets. These results suggest autophagy or endocytosis abnormalities and provide evidence for multiple types of dense bodies in carcinoid platelets.

Effect of polylysine on the activation of prothrombin. Polylysine substitutes for calcium ions and factor V in the factor Xa catalyzed activation of prothrombin

Polylysine has been demonstrated to dramatically accelerate the rate of the factor Xa catalyzed activation of both prothrombin and prethrombin 1. Under the present experimental conditions (pH 8.0, 23 C), no detectable activation of prothrombin or prethrombin 1 occurs with either factor Xa or polylysine alone. The activation of prethrombin 2, the direct precursor of alpha-thrombin, by factor Xa is not stimulated by polylysine. The activation of either prothrombin or prethrombin 1 by factor Xa in the presence of polylysine is partially inhibited by the presence of 5 mM CaCl2. Electrophoretic analysis in sodium dodecyl sulfate showed that the products that were formed in the above activation system comigrated with the reaction products derived from prothrombin activated by factor Xa in the presence of calcium ions and phospholipid. It is suggested that polylysine stimulates the factor Xa-catalyzes activation of prothrombin by replacing the combination of calcium ions and factor V.

Substitution of lanthanide ions for calcium ions in the activation of bovine prothrombin by activated factor X. High affinity metal-binding sites of prothrombin and the derivatives of prothrombin activation

The substitution of lanthanide ions for Ca(II) in the Ca(II)-binding sites of prothrombin and the derivatives of prothrombin activation and in the metal-dependent conversion of prothrombin or prethrombin 1 to thrombin was studied at pH 6.8. Gd(III), Tb(III), La(III), Dy(III), Pr(III), Sm(III), and Ce(III) may be substituted for Ca(II) in the generation of thrombin from prothrombin or prethrombin 1 by activated factor X. The rates of thrombin generation in the presence of optimal concentrations of Gd(III) were about 25% for prothrombin and prethrombin 1 compared to the rate of thrombin generation with optimal concentrations of Ca(II). Maximal rates of thrombin generation were observed at 20 muM Gd(III) using prothrombin as substrate, compared to 10 muM Gd(III) when prethrombin 1 was employed. Using the steady state rate-dialysis method, the high affinity metal-binding sites of prothrombin and the products formed during prothrombin activation were characterized using 153Gd(III). Prothrombin has two high affinity binding sites for Gd(III) (Kd = 0.75 muM). Prethrombin 1 and prethrombin 2 each bind one Gd(III) tightly (Kd = 1.10 muM and 0.81 muM, respectively). Fragment 1, the phospholipid-binding portion of prothrombin, has two sites which bind Gd(III) tightly (Kd 0.16 muM). Fragment 2 has no high affinity metal-binding sites, but has intermediate affinity metal-binding sites (Kd greater than 1.6 muM). Thrombin has numerous high affinity binding sites (Kd less than 0.1 muM), suggesting that the conversion of prethrombin 2 to thrombin is associated with a significant change in tertiary structure. These results indicate that Gd(III) binds tightly to the metal-binding sites of these proteins and can substitute for Ca(II) in metal-dependent prothrombin activation. In the activation of prothrombin by activated factor X, these data suggest that Ca(II) is required for metal-dependent factor V and phospholipid binding and not as a cofactor in enzyme catalysis.