Anticoagulant activity of a sulfated polysaccharide from the green alga Arthrospira platensis

Background

The polysaccharide of culture medium from Arthrospira platensis was extracted by ultrafiltration, partially characterized and assayed for anticoagulant activity.

Methods

The crude polysaccharidic fraction was fractionated by anion exchange chromatography on DEAE-cellulose, subjected to acetate cellulose electrophoresis and characterized by physicochemical procedures. The anticoagulant effect of the ultrafiltrated polysaccharide was checked by several coagulation tests.

Results

Anion exchange chromatography revealed in the whole ultrafiltrated polysaccharidic fraction the occurrence of a sulfated spirulan-like component designated PUF2. The average molecular weight of PUF2 was determined by size exclusion chromatography combined with multi-angle light scattering (SEC-MALS) and viscosimetry and was 199 kDa and the sulfate content was 20% weight/dry weight. The physicochemical characterization indicated the occurrence of rhamnose (49.7%), galacturonic and glucuronic acid (32% of total sugar). The anticoagulant effect of this sulfated polysaccharide was mainly due to the potentiation of thrombin inhibition by heparin cofactor II and was 4-times higher than that of the porcine dermatan sulfate whereas it had no effect on anti-Xa activity.

Conclusions

An ultrafiltrated sulfated polysaccharide, likely a calcium spirulan was obtained from the culture medium of A. platensis and showed an anticoagulant activity mediated by heparin cofactor II.

General significance

Old culture medium of A. platensis may represent an important source for the spirulan-like PUF2 which was endowed with potentially useful anticoagulant properties whereas its obtention by ultrafiltration may represent an extraction procedure of interest.     

Sulfated polysaccharide purified from <Emphasis Type="BoldItalic">Ecklonia cava</Emphasis> accelerates antithrombin III-mediated plasma proteinase inhibition

Surface plasmon resonance is an important technique for studying molecular interactions and was used to investigate the molecular interaction of anticoagulant sulfated polysaccharides purified from an enzymatic hydrolysate of the brown alga Ecklonia cava (ECA) with blood coagulation factors. In a direct binding assay, binding affinity between ECA/antithrombin III (ATIII) and activated blood coagulation factors was in the order: factor VIIa (FVIIa) > factor Xa (FXa) > thrombin (FIIa); kinetic analysis determined K _D values of ECA for FVIIa, FXa, and FIIa of 15.1, 45.0 and 65.0 nM, respectively. Therefore, ECA strongly and selectively (FVII, FX, and FII) enhanced ATIII-mediated coagulation factor inhibition in both the extrinsic and common coagulation pathways. This may contribute to its high anticoagulant activity in vitro. The low cytotoxicity of ECA to venous endothelial cell line (ECV-304) also expands its value in future in vivo studies. However, to utilize it as a model for novel anticoagulant agents, its possible interference with other anticoagulant mechanisms must be addressed.     

A novel anticoagulant protein with high affinity to blood coagulation factor Va from Tegillarca granosa

A novel inhibitory protein against blood coagulation factor Va (FVa) was purified from muscle protein of granulated ark (Tegillarca granosa, order Arcoida, marine bivalvia) by consecutive FPLC method using anion exchange and gel permeation chromatography. In the results of ESIQTOF tandem mass analysis and database research, it was revealed that the purified T. granosa anticoagulant protein (TGAP) has 7.7 kDa of molecular mass and its partial sequence, HTHLQRAPHPNALGYHGK, has a high identity (64%) with serine/threonine kinase derived from Rhodopirellula baltica (order Planctomycetales, marine bacteria). TGAP could potently prolong thrombin time (TT), corresponding to inhibition of thrombin (FIIa) formation. Specific factor inhibitory assay showed that TGAP inhibits FVa among the major components of prothrombinase complex. In vitro assay for direct-binding affinity using surface plasmon resonance (SPR) spectrometer indicated that TGAP could be directly bound with FVa. In addition, the binding affinity of FVa to FII was decreased by addition of TGAP in dose-dependant manner (IC50 value = 77.9 nM). These results illustrated that TGAP might interact with a heavy chain of FVa (FVa(H)) bound to FII in prothrombin complex. The present study elucidated that non-cytotoxic T. granosa anticoagulant protein (TGAP) bound to FVa can prolong blood coagulation time by inhibiting conversion of FII to FIIa in blood coagulation cascade. In addition, TGAP did not significantly (P < 0.05) show fibrinolytic activity and cytotoxicity on venous endothelial cell line (ECV 304).     

Anticoagulant activity of sulfated polysaccharide isolated from fermented brown seaweed Sargassum fulvellum

A sulfated polysaccharide with anticoagulant properties was isolated from the fermented brown seaweed Sargassum fulvellum. Freeze-dried S. fulvellum was fermented in an incubator for 10^th week at 25°C to convert seaweed macromolecules into anticoagulant sulfated polysaccharides (ASP). Anticoagulant activity was determined by an activated partial thromboplastin time (APTT) test using citrated human blood plasma. The 8^th week S. fulvellum crude seaweed extract (SWE) exhibited the highest blood anticoagulant activity. Therefore, 8^th week crude SWE was used for purification of ASP by two steps; DEAE cellulose anion-exchange followed by Sepharose 4B chromatography. The isolated ASP showed a single spot on agarose gel electrophoresis, which confirmed the purification status of our ASP. Polyacrylamide gel electrophoresis (PAGE) analysis showed that the molecular mass of the purified ASP was between 8 and 20 kDa. Polysaccharide and sulfate concentrations of the purified ASP were 180 and 29.70 μg mL⁻¹ respectively. ASP recovery was 1.32% (w/w) from the crude polysaccharide applied to the DEAE column. Purified ASP had a pH of 3.86 and was considered an acidic polysaccharide. Moreover, both ASP and heparin showed a relative clotting factor of 27.47 at the concentrations of 180 and 60 μg mL⁻¹ respectively. Therefore, S. fulvellum ASP can be considered a weaker anticoagulant than heparin. Results of the APTT, PT, and TT clotting assays showed that ASP was able to inhibit both intrinsic and extrinsic blood coagulation pathways. Finally, this study established a feasible and simple experimental protocol to isolate anticoagulant from fermented seaweeds leading to potential further development of anticoagulant agent for the pharmaceutical industry.     

Structure and anticoagulant activity of a sulfated galactan from the red alga, Gelidium crinale. Is there a specific structural requirement for the anticoagulant action?

Marine red algae are an abundant source of sulfated galactans with potent anticoagulant activity. However, the specific structural motifs that confer biological activity remain to be elucidated. We have now isolated and purified a sulfated galactan from the marine red alga, Gellidium crinale. The structure of this polysaccharide was determined using NMR spectroscopy. It is composed of the repeating structure -4-alpha-Galp-(1-->3)-beta-Galp1--> but with a variable sulfation pattern. Clearly 15% of the total alpha-units are 2,3-di-sulfated and another 55% are 2-sulfated. No evidence for the occurrence of 3,6-anhydro alpha-galactose units was observed in the NMR spectra. We also compared the anticoagulant activity of this sulfated galactan with a polysaccharide from the species, Botryocladia occidentalis, with a similar saccharide chain but with higher amounts of 2,3-di-sulfated alpha-units. The sulfated galactan from G. crinale has a lower anticoagulant activity on a clotting assay when compared with the polysaccharide from B. occidentalis. When tested in assays using specific proteases and coagulation inhibitors, these two galactans showed significant differences in their activity. They do not differ in thrombin inhibition mediated by antithrombin, but in assays where heparin cofactor II replaces antithrombin, the sulfated galactan from G. crinale requires a significantly higher concentration to achieve the same inhibitory effect as the polysaccharide from B. occidentalis. In contrast, when factor Xa instead of thrombin is used as the target protease, the sulfated galactan from G. crinale is a more potent anticoagulant. These observations suggest that the proportion and/or the distribution of 2,3-di-sulfated alpha-units along the galactan chain may be a critical structural motif to promote the interaction of the protease with specific protease and coagulation inhibitors.     

A novel blood coagulation factor IX/factor X-binding protein with anticoagulant activity from the venom of Trimeresurus flavoviridis (Habu snake): isolation and characterization

Using affinity chromatography on a column of factor X-Cellulofine, we have isolated a novel blood coagulation factor X-binding protein with anticoagulant activity from the venom of Trimeresurus flavoviridis (Habu snake). This anticoagulant protein was also purified by chromatography on Sephadex G-75 and S-Sepharose Fast Flow. The yield of the purified protein was approximately 16 mg from 400 mg of crude venom. The purified protein gave a single band on both analytical alkaline disc-gel electrophoresis and SDS-PAGE. This protein had a relative molecular weight (Mr) after SDS-PAGE of 27,000 before reduction of disulfide bonds and 14,000 after reduction of disulfide bonds. The protein prolonged the clotting time induced by kaolin or factor Xa. In the presence of Ca2+, it formed a complex with factor X, the molar ratio being 1 to 1. Similar complex formation was observed with factor Xa and factor IX/factor IXa, but not with other vitamin K-dependent coagulation factors, i.e., prothrombin, factor VII, protein C, protein S, and protein Z. The interaction of this anticoagulant protein with factor IX/factor X was dependent on gamma-carboxyglutamic acid (Gla) domains, since Gla-domainless derivatives of factor X and factor IXa beta' did not interact with this anticoagulant protein.     

Purified protein S contains multimeric forms with increased APC-independent anticoagulant activity

Protein S, the cofactor of activated protein C (APC), also expresses anticoagulant activity independent of APC by directly inhibiting prothrombin activation via interactions with factor Xa, factor Va, and phospholipids. In different studies, however, large variations in APC-independent anticoagulant activities have been reported for protein S. The investigation presented here shows that within purified protein S preparations different forms of protein S are present, of which a hitherto unrecognized form (<5% of total protein S) binds with high affinity to phospholipid bilayers (K(d) < 1 nM). The remaining protein S (>95%) has a low affinity (K(d) = 250 nM) for phospholipids. Using their different affinities for phospholipids, separation of the forms of protein S was achieved. Native polyacrylamide gel electrophoresis demonstrated that the form of protein S that binds to phospholipids with low affinity migrated as a single band, whereas the high-affinity protein S exhibited several bands that migrated with reduced mobility. Size-exclusion chromatography revealed that the slower-migrating bands represented multimeric forms of protein S. Multimeric protein S (<5% of total protein S) appeared to have a 100-fold higher APC-independent anticoagulant activity than the abundant form of protein S. Comparison of purified protein S preparations that exhibited a 4-fold difference in APC-independent anticoagulant activity showed that the ability to inhibit prothrombin activation correlated with the content of multimeric protein S. Multimeric protein S could not be identified in normal human plasma, and it is therefore unlikely that this form of protein S contributes to the APC-independent anticoagulant activity of protein S that is observed in plasma.     

Isolation and characterization of an anticoagulant from the salivary glands of the tick, Ornithodoros savignyi (Acari: Argasidae)

An inhibitor of activated coagulation factor X (fXa) was isolated from salivary gland extracts prepared from Ornithodoros savignyi using a two-step procedure, involving reversed-phase high-performance liquid chromatography (RP-HPLC) and diethylaminoethyl (DEAE) ion-exchange chromatography. From its behaviour during DEAE chromatography it could be deduced that it possesses an acidic pI (4.6). Capillary zone electrophoresis (CZE) of the purified inhibitor showed it to be homogeneous. The molecular mass was determined as 12 kDa using capillary gel electrophoresis (CGE) and as 7183.4 using laser desorption mass spectrometry (LDMS). The N-terminal amino acid sequence (residues 1–12) was determined and found to share a 66% identity with tick anticoagulant peptide (TAP). The O. savignyi peptide is a slow, tight-binding inhibitor of fXa (K _i=0.83±0.10 nM). The interaction of the fXa-inhibitor was found to be competitive and dependent on ionic strength. Preliminary investigations show that the inhibitor may be specific for fXa.Deceased.     

Chemical characteristic of an anticoagulant-active sulfated polysaccharide from Enteromorpha clathrata

A sulfated polysaccharide FEP from marine green alga Enteromorpha clathrata was extracted with hot water and further purified by ion-exchange and size-exclusion chromatography. Results of chemical and spectroscopic analyses showed that FEP was a high arabinose-containing sulfated polysaccharide with sulfate ester of 31.0%, and its average molecular weight was about 511kDa. The backbone of FEP was mainly composed of (1→4)-linked β-l-arabinopyranose residues with partially sulfate groups at the C-3 position. In vitro anticoagulant assay indicated that FEP effectively prolonged the activated partial thromboplastin time and thrombin time. The investigation demonstrated that FEP was a novel sulfated polysaccharide with different chemical characteristics from other sulfated polysaccharides from marine algae, and could be a potential source of anticoagulant.     

尖吻蝮蛇毒内一种新抗凝血因子ACF II 的纯化及特性

利用阴离子交换层析、凝胶过滤及阳离子交换层析三步方法, 从皖南尖吻蝮蛇毒中分离纯化到一个新的抗凝血因子ＡＣＦＩＩ（ａｎｔｉｃｏａｇｕｌａｔｉｏｎ ｆａｃｔｏｒＩＩ） 。纯化的ＡＣＦＩＩ在ＰＡＧＥ、ＳＤＳＰＡＧＥ和ＩＥＦＰＡＧＥ图谱上均呈单一区带。ＡＣＦＩＩ由两条分子量为１４．６ ｋＤ 的肽链通过二硫键连接在一起, 其等电点为７．０。ＡＣＦＩＩ具有显著的抗凝血活性, 在体外延长ＰＰＴ 时间的最终浓度为０ ．４ ｍｇ／Ｌ。ＡＣＦＩＩ不具有类凝血酶活性、磷脂酶Ａ２ 活性和纤溶活性,也没有出血活性和毒性, 是一种潜在的高效抗凝药物。     

Isolation of a pure octadecasaccharide with antithrombin activity from an ultra-low-molecular-weight heparin

Heparin and low-molecular-weight heparins (LMWHs) are anticoagulant drugs that mainly inhibit the coagulation cascade by indirectly interacting with factor Xa and factor IIa (thrombin). Inhibition of factor Xa by antithrombin (AT) requires the activation of AT by specific pentasaccharide sequences containing 3-O-sulfated glucosamine. Activated AT also inhibits thrombin by forming a stable ternary complex of AT, thrombin, and a polysaccharide (requires at least an 18-mer/octadeca-mer polysaccharide). The full structure of any naturally occurring octadecasaccharide sequence has yet to be determined. In the context of the development of LMWH biosimilars, structural data on such important biological mediators could be helpful for better understanding and regulatory handling of these drugs. Here we present the isolation and identification of an octadecasaccharide with very high anti-factor Xa activity (∼3 times higher than USP [U.S. Pharmacopeia] heparin). The octadecasaccharide was purified using five sequential chromatographic methods with orthogonal specificity, including gel permeation, AT affinity, strong anion exchange, and ion-pair chromatography. The structure of the octadecasaccharide was determined by controlled enzymatic sequencing and nuclear magnetic resonance (NMR). The isolated octadecasaccharide contained three consecutive AT-binding sites and was tested in coagulation assays to determine its biological activity. The isolation of this octadecasaccharide provides new insights into the modulation of thrombin activity.     

The structure-anticoagulant activity relationships of sulfated lacquer polysaccharide: effect of carboxyl group and position of sulfation

Regiospecific oxidation of the primary hydroxyl groups in lacquer polysaccharide (LPL, Mw 6.85 x 10(4)) and its NaIO4 oxidation derivatives (LPLde) to C-6 carboxy groups was achieved with NaOCl in the presence of Tempo and NaBr. Sulfate groups were incorporated into the oxidated polysaccharides using Py.SO3 complex as a reagent. Reactivity of polysaccharide hydroxyl group was C-6 > C-2 > C-4. Sulfate groups were mainly linked to the second hydroxy at C-2 in the products. The results of APTT assay showed after incorporation of carboxyl groups into lacquer polysaccharides, the intrinsic coagulation pathway was promoted, and all sulfated polysaccharides had very weak anticoagulant activity within the scope of studied DS (0.39-1.11). These indicated that carboxyl groups and sulfate groups had the synergistic action. At the same time, the anticoagulant activity increased very slowly with the DS in the second hydroxy. This indicated that 6-O-SO3- in the side chains took an important role in the anticoagulant activity.     

A novel anticoagulant protein from Scapharca broughtonii

An anticoagulant protein was purified from the edible portion of a blood ark shell, Scapharca broughtonii, by ammonium sulfate precipitation and column chromatography on DEAE-Sephadex A-50, Sephadex G- 75, DEAE-Sephacel, and Biogel P-100. In vitro assays with human plasma, the anticoagulant from S. broughtonii, prolonged the activated partial thromboplastin time (APTT) and inhibited the factor IX in the intrinsic pathway of the blood coagulation cascade. But, the fibrin plate assay did not show that the anticoagulant is a fibrinolytic protease. The molecular mass of the purified S. broughtonii anticoagulant was measured to be about 26.0 kDa by gel filtration on a Sephadex G-75 column and SDSPAGE under denaturing conditions. The optimum activity in the APTT assay was exhibited at pH 7.0-7.5 and 40-45 degrees C in the presence of Ca(2+).     

Anticoagulant activity of M-LAO, l-amino acid oxidase purified from Agkistrodon halys blomhoffii, through selective inhibition of factor IX

One of haemorrhagic toxins present in snake venoms is l-amino acid oxidase (LAO), which catalyzes the oxidative deamination of l-amino acids with the generation of hydrogen peroxide. Although it is widely accepted that LAO alters platelet function, the effects of LAO on human blood coagulation remain largely unknown. The present study demonstrated, for the first time, that M-LAO, LAO purified from the venom of Agkistrodon halys blomhoffii (Japanese mamushi), possesses an anticoagulant activity. Thrombelastography (TEG) showed that M-LAO significantly delayed the onset and the progress of the coagulation process. In addition, the enzyme prolonged the activated partial thromboplastin time (aPTT) dose-dependently, but had little effect on the prothrombin time (PT), suggesting that its principal activity was mediated in the intrinsic coagulation pathway. Furthermore, M-LAO reduced factor IX procoagulant activity in a dose-dependent manner and did not affect other coagulation factors. These results indicate that M-LAO has an anticoagulant activity that impairs the intrinsic clotting by inhibiting factor IX.     

Anticoagulant activity of marine green and brown algae collected from Jeju Island in Korea

Twenty-two algal species were evaluated for their potential anticoagulant activities. Hot water extracts from selected species, Codium fragile and Sargassum horneri showed high activated partial thromboplastin time (APTT). Ultraflo extract of C. fragile and S. horneri exhibited the most potent anticoagulant activity. Furthermore, in both algal species, active compounds were mainly concentrated in >30kDa faction. The crude polysaccharide fraction (>30kDa; CpoF) of C. fragile composed of approximately 80% carbohydrate and approximately 19% of protein; the crude polysaccharide fraction (>30kDa; CpoF) of S. horneri was composed of 97% of carbohydrate and approximately 2% of protein. Therefore, most probably the active compound, or compounds of the algal species were related to high molecular weight polysaccharide, or a complex form with carbohydrate and protein (proteoglycan).     

A potent insect chitinase inhibitor of fungal origin

A water-soluble polysaccharide was isolated from the culture filtrate of a fungal strain, Sphaeropsis sp. TNPT116-Cz, as a novel insect chitinase inhibitor. It was purified to chromatographic homogeneity by ethanol precipitation, anion-exchange and gel filtration chromatography. Its molecular weight was estimated to be 16 kDa by gel filtration HPLC. Monosaccharide analysis showed that it contained glucose, galactose, N-acetylglucosamine and a deoxysugar. This polysaccharide showed potent and specific inhibitory activity against Spodoptera litura chitinase with an IC50 value of 28 nM.     

库克Noni果汁多糖含量及分子量测定

建立测定库克Noni果汁中多糖含量及分子量的方法。通过醇沉法分离Noni果汁多糖,进一步分离纯化得到均一多糖组分;用精制Noni果汁多糖测得该多糖对葡萄糖的换算因子,对多糖含量进行定量测定;并通过SE-HPLC(Size Exclusion-High Performance Liquid Chromatography)法测定了该多糖的相对分子量。结果表明,多糖含量测定方法简便可行,供试液在4 h内显色稳定,重现性较好,平均回收率为99.3%,RSD为1.93%(n=3);测得该多糖的相对分子量为1140 KDa。     

Immunoaffinity purification and characterization of lipoprotein-associated coagulation inhibitors from Hep G2 hepatoma, Chang liver, and SK hepatoma cells. A comparative study

A polyclonal antibody against a synthetic peptide corresponding to amino acids 3-25 of mature lipoprotein-associated coagulation inhibitor (LACI) was raised in rabbits. The antibody was used to study the production of LACI by Hep G2 hepatoma, Chang liver, and SK hepatoma cells, and to purify LACI from the culture media. By using an amidolytic assay for factor Xa, it was found that the culture media from these liver-derived cell lines contain inhibitors of factor Xa. In Hep G2 hepatoma culture medium, approximately 50% of Xa inhibitory activity was due to LACI. In the Chang liver and SK hepatoma culture media over 95% of the Xa inhibitory activity was due to LACI. The LACIs were purified from these media by immunoaffinity chromatography on an anti-LACI-lg-Sepharose 4B column and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified LA-CIs varied in molecular weight depending on whether the media were concentrated before chromatography. An Mr approximately 38,000 LACI was obtained by chromatography of unconcentrated media. Chromatography of concentrated media yielded a LACI of Mr approximately 35,000 with the same amino-terminal sequence, suggesting partial proteolysis in the carboxyl-terminal region. In addition, an Mr approximately 25,000 form of LACI was also present. The purified Mr approximately 38,000 and approximately 35,000 LACI species from the above cells possess similar specific activities when measured by an anti-Xa/amidolysis assay. To study the role of LACI in the control of coagulation, pooled human plasma was depleted of LACI antigen by immunoaffinity absorption and reconstituted with varying amounts of purified LACI to examine the effect on tissue factor (TF)-induced coagulation. LACI depletion shortens the time of TF-induced clotting of plasma and the clotting time is linearly related to the LACI concentration after reconstitution. These results suggest that LACI plays an important role in limiting TF-induced coagulation in human plasma. Comparison of the potencies of various purified LACIs in the prolongation of TF-induced coagulation revealed that LA-CIs from different sources are not equivalent. The plasma LACI, SK hepatoma LACI, and Chang liver LACI are approximately 7-, 6-7, and 1.3-fold higher in specific activity than Hep G2 hepatoma LACI in the TF-induced clotting assay when compared on an anti-Xa/amidolysis unit basis, suggesting possible differences in post-translational modification of these LA-CIs.     

Anticoagulant activity of M-LAO,L-amino acid oxidase purified from Agkistrodon halys blomhoffii,through selective inhibition of factor IX

One of haemorrhagic toxins present in snake venoms is L-amino acid oxidase (LAO), which catalyzes the oxidative deamination of L-amino acids with the generation of hydrogen peroxide. Although it is widely accepted that LAO alters platelet function, the effects of LAO on human blood coagulation remain largely unknown. The present study demonstrated, for the first time, that M-LAO, LAO purified from the venom of Agkistrodon halys blomhoffii (Japanese mamushi), possesses an anticoagulant activity. Thrombelastography (TEG) showed that M-LAO significantly delayed the onset and the progress of the coagulation process. In addition, the enzyme prolonged the activated partial thromboplastin time (aPTT) dose-dependently, but had little effect on the prothrombin time (PT), suggesting that its principal activity was mediated in the intrinsic coagulation pathway. Furthermore, M-LAO reduced factor IX procoagulant activity in a dose-dependent manner and did not affect other coagulation factors. These results indicate that M-LAO has an anticoagulant activity that impairs the intrinsic clotting by inhibiting factor IX.     

Lyso-Sulfatide Binds Factor Xa and Inhibits Thrombin Generation by the Prothrombinase Complex

Blood coagulation reactions are strongly influenced by phospholipids, but little is known about the influence of sphingolipids on coagulation mechanisms. Lysosulfatide (lyso-SF) (sulfogalactosyl sphingosine) prolonged factor Xa (fXa) 1-stage plasma clotting assays, showing it had robust anticoagulant activity. In studies using purified clotting factors, lyso-SF inhibited >90% of prothrombin (II) activation for reaction mixtures containing fXa/factor Va (fVa)/II, and also inhibited II activation generation by fXa/ phospholipids and by Gla-domainless-fXa/fVa/phospholipids. When lyso-SF analogs were tested, results showed that N-acetyl-sulfatide was not anticoagulant, implying that the free amine group was essential for the anticoagulant effects of lyso-SF. Lyso-SF did not inhibit fXa enzymatic hydrolysis of small peptide substrates, showing it did not directly inhibit the fXa activity. In surface plasmon resonance studies, lyso-SF bound to immobilized inactivated fXa as well as inactivated Gla-domainless-fXa. Confirming this lyso-SF:fXa interaction, fluorescence studies showed that fluorescently-labeled-fXa in solution bound to lyso-SF. Thus, lyso-SF is an anticoagulant lipid that inhibits fXa when this enzyme is bound to either phospholipids or to fVa. Mechanisms for inhibition of procoagulant activity are likely to involve lyso-SF binding to fXa domain(s) that are distinct from the fXa Gla domain. This suggests that certain sphingolipids, including lyso-SF and some of its analogs, may down-regulate fXa activity without inhibiting the enzyme’s active site or binding to the fXa Gla domain.