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Suppose G is a reductive algebraic group, T is a Cartan subgroup of G, N = Norm ( T ) , and W = N / T is the Weyl group. If w ∈ W has order d, it is natural to ask about the orders lifts of w to N. It is straightforward to see that the minimal order of a lift of w has order d or 2d, but it can be a subtle question which holds. We first consider the question of when W itself lifts to a subgroup of N (in which case every element of W lifts to an element of N of the same order). We then consider two natural classes of elements: regular and elliptic. In the latter case all lifts of w are conjugate, and therefore have the same order. We also consider the twisted case.

Let G G be a connected, simple algebraic group over an algebraically closed field. There is a partition of the wonderful compactification G ¯ \bar {G} of G G into finite many G G -stable pieces, which was introduced by Lusztig. In this paper, we will investigate the closure of any G G -stable piece in G ¯ \bar {G} . We will show that the closure is a disjoint union of some G G -stable pieces, which was first conjectured by Lusztig. We will also prove the existence of cellular decomposition if the closure contains finitely many G G -orbits.

The observation accuracy of space camera targ eted on ground objects is directly affected by th e pointing deviation of the two dimensional scan mirror. A plane model of the scan mirror’s normal trajectory is established when scan mirror is rotating along the rolling axis while the pitching axis remain s still. The pointing accuracy of scan mirror cross the track direction is measured with the plane model. A cone model of the scan mirror’s normal trajectory is established when scan mirror is rotating along the pitc hing axis while the rolling axis remains still. The pointing accuracy of scan mirror along the track direction is measured with the plan e model. The nonorthogonality of shafting of the rolling axis and the pitching axis is measured with the two models. Data processing results are feedback to pointing controller to correct the input signal of resolver, until the pointing accuracy of scan mirror meets the requirement. The experimental results indicate that the models of measuring the pointing accuracy of scan mirror are accurate and the data processing algorithm is feasible. The testing precision reached 10

Programmable imager spectrometer can provide flexible data by changing the spectrum section number, central wavelength, spectral width and spatial resolution in orbit. Spectral calibration of imaging spectrometer plays an important role for acquiring accurate spectrum, two spectral calibration types are in essence: wavelength calibration and Full-width-half-maximum (FWHM). Base on the character of programmable imager spectrometer, designed a set of spectral calibration system. Wavelength calibration realized by utilizing the Monochromatic light of high precision monochromator, during the test, changed output parameters of monochromator according to the spectral bandwidth of imager spectrometer. The FWHM is constructed by a set of variable narrow spectrum lines that is output by tunable laser. Gaussian fitting algorithm is used to determine center wavelength and the FWHM of the characteristic spectrum line, Spectral pixels are calibrated by quadratic polynomial, standard spectroscopic lamp is used to verify wavelength calibration result accuracy. The calibration result indicates that FWHM is better than 2nm, the wavelength uncertainty is less than 0.6nm, meet the calibration requirements of programmable imaging spectrometer.

We give a definition of character sheaves on the group compactification which is equivalent to Lusztig's definition in \cite{L3}. We also prove some properties of the character sheaves on the group compactification., 22 pages. Final version

In this paper, we give explicit descriptions of the centers and cocenters of 0-Hecke algebras associated to finite Coxeter groups.

Activated protein C (APC) requires both Ca2+ and Na+ for its optimal catalytic function. In contrast to the Ca2+-binding sites, the Na+-binding site(s) of APC has not been identified. Based on a recent study with thrombin, the 221-225 loop is predicted to be a potential Na+-binding site in APC. The sequence of this loop is not conserved in trypsin. We engineered a Gla domainless form of protein C (GDPC) in which the 221-225 loop was replaced with the corresponding loop of trypsin. We found that activated GDPC (aGDPC) required Na+ (or other alkali cations) for its amidolytic activity with dissociation constant (Kd(app)) = 44.1 +/- 8.6 mM. In the presence of Ca2+, however, the requirement for Na+ by aGDPC was eliminated, and Na+ stimulated the cleavage rate 5-6-fold with Kd(app) = 2.3 +/- 0.3 mM. Both cations were required for efficient factor Va inactivation by aGDPC. In the presence of Ca2+, the catalytic function of the mutant was independent of Na+. Unlike aGDPC, the mutant did not discriminate among monovalent cations. We conclude that the 221-225 loop is a Na+-binding site in APC and that an allosteric link between the Na+ and Ca2+ binding loops modulates the structure and function of this anticoagulant enzyme.

Human protein S (PS) potentiates the anticoagulant activity of human but not bovine activated protein C (APC), whereas bovine PS is a cofactor to APC from both species. The structural requirements for the specificity of the APC cofactor function of human PS are located in its thrombin-sensitive region (TSR) and the first epidermal growth factor (EGF1)-like module. To elucidate which residues in these two modules determine the specificity of the APC cofactor activity, 41 human PS mutants were expressed. All mutants were cofactors to human APC and some also to bovine APC. Residues in TSR (positions 49 and 52) and EGF1 (residues 97 and 106) together determined the specificity of the APC cofactor function, whereas substitution of individual residues did not change specificity. Bovine PS, and mutants expressing cofactor activity to bovine APC, stimulated phospholipid binding of bovine APC. In contrast, human PS and mutants lacking cofactor activity to bovine APC failed to support binding of bovine APC to phospholipids. These data indicate that residues in TSR and EGF1 cause the specificity of the APC cofactor activity and support the concept that key residues in these two modules interact with APC on the phospholipid surface.

An increased ratio between serum levels of immunoreactive anionic and cationic trypsin is a common finding in many forms of pancreatic disease. Experimental studies have shown that increased stimulation with cholecystokinin (CCK) leads to an increase in the ratio between the pancreatic content of anionic and cationic trypsin. To study whether this effect is caused by increased pancreatic synthesis of anionic trypsin in relation to cationic trypsin we studied the levels of mRNA for anionic and cationic trypsinogen in pancreatic extracts from rats exposed to increased CCK levels through chronic subcutaneous administration of CCK. Northern blot and slot blot hybridization techniques were used. The ratio between mRNAs for anionic and cationic trypsin was significantly higher in CCK-treated rats: median level, 2.04 (range, 1.33-4.08) versus a median level of 1.15 (range, 0.97-2.17) in the control group: P0.01. These findings support the view that chronic CCK stimulation leads to the increased synthesis of anionic trypsinogen compared to cationic trypsinogen.

Protein S is an anticoagulant vitamin-K-dependent plasma glycoprotein, which acts as a cofactor to activated protein C in the degradation of coagulation factors Va and VIIIa. It has been proposed that protein S has an additional function as a growth factor. Protein S and a structurally similar protein, Gas6, have been found to stimulate members of the Axl/Sky family of receptor tyrosine kinases. Human Gas6 is able to activate Axl and Sky. In contrast, while bovine protein S activates human Sky and its murine homologue, human protein S activates murine Sky but not the human receptor. In the present investigation, we studied the structural background of this species difference. Using protein S chimeras with domains from human and bovine origin, we found that only those chimeras with the steroid-hormone-binding globulin-like (SHBG) region from bovine protein S activate human Sky, indicating that the SHBG region is essential for the interaction. This observation was confirmed by inhibition of Sky phosphorylation by C4b-binding protein, a plasma protein that interacts tightly with the SHBG region of protein S. Another chimeric molecule, composed of the N-terminal 4-carboxyglutamic-acid-containing domain (Gla domain) and the two epidermal-growth-factor-like domains of human factor IX, and the SHBG region of bovine protein S, stimulated the receptor less efficiently. Antibodies directed against the Gla domain of protein S, inhibited the activation of human Sky by bovine protein S. These results indicate that the N-terminal domains of protein S are not essential for activation of the receptor, but contribute to the affinity of the interaction. Our data suggest that protein S might be a ligand of Sky in some species despite the lack of activity of human protein S on human Sky. The bovine/human protein S species difference will be a useful model to establish the structural requirements for the interaction between Sky and its ligands.

Expression of the endothelial cell protein C receptor (EPCR) gene in mammalian cells imparts the capacity to bind activated protein C (APC) or protein C. Immunochemical analysis of CCD41, apparently the murine homologue of EPCR, suggested centrosomal localization, raising questions about the location of the EPCR gene product and its role in protein C binding. In this study, we express a soluble form of EPCR, demonstrate EPCR expression on the cell surface, and direct binding between soluble EPCR and protein C/APC. Affinity purified polyclonal and a monoclonal antibody against EPCR bound to the cell surface of EPCR-transfected cells but not to control cells. A 49-kDa protein, a mass similar to soluble EPCR, was immunoprecipitated from the cell surface of endothelium and cells transfected with human EPCR but not from control cells. The FLAG™ antibody and APC bound to cells expressing an EPCR construct containing the FLAG™ epitope located in a putative extracellular domain, whereas an EPCR construct truncated just before the putative transmembrane domain produced only soluble EPCR antigen. Soluble EPCR inhibited APC binding to EPCR expressing cells in a concentration-dependent fashion, Kd(app) = 29 nM and bound to immobilized protein C in a Ca2+-dependent fashion. Thus, EPCR is a type 1 transmembrane protein that binds directly to APC.

In this paper, we study the set $B(G, \{\mu\})$ of acceptable elements for any $p$-adic group $G$. We show that $B(G, \{\mu\})$ contains a unique maximal element and the maximal element is represented by an element in the admissible subset of the associated Iwahori-Weyl group.

Vitamin-K-dependent protein S is an anticoagulant plasma protein functioning as a cofactor to activated protein C (APC) in the degradation of factors Va and VIIIa. The APC-cofactor function of protein S is species specific, as human protein S potentiates the anticoagulant activity of human but not that of bovine APC, whereas bovine protein S is a cofactor to APC from both species. To elucidate which modules in protein S determine the species specificity, in vitro mutagenesis was used to construct six recombinant chimeric molecules between human and bovine protein S. Wild-type human and bovine protein S and the chimeras were expressed in 293 cells and the recombinant proteins purified by monoclonal antibody affinity chromatography. The recombinant proteins were found to be post-translationally modified, they bound C4b-binding protein and were functionally active as cofactors to APC. Chimeras having both the thrombin-sensitive region (TSR) and the first epidermal-growth-factor-(EGF)-like module of bovine origin expressed APC-cofactor activity similar to that of bovine protein S. Those chimeras, in which TSR or EGF1 derived from different species, manifested APC-cofactor activity similar to that of human protein S, i.e. they did not express cofactor activity to bovine APC. These data indicate that sequence differences in the TSR and EGF1 of human and bovine protein S cause the species specificity of the APC-cofactor activity. The data support the concept that these two modules of protein S interact with APC on the surface of negatively charged phospholipids.

Vitamin-K-dependent protein S is an anticoagulant plasma protein which functions as cofactor to activated protein C (APC) in the degradation of coagulation factors Va and VIIIa. In addition, it interacts with C4b-binding protein (C4BP), a regulator of the complement system. Using a human protein S cDNA clone as probe, cDNA clones for rabbit protein S were isolated from a rabbit liver cDNA library. The cDNA sequence encoded the mature protein S and 12 residues of the leader sequence. The amino acid sequence of the single-chain 634-amino-acid-residue-long rabbit protein S molecule was 82% and 81% identical to those of human and bovine protein S, respectively. Northern blotting demonstrated protein S mRNA not only in liver but also in reproductive organs (testis, ovary and uterus), in lung and brain. Recombinant rabbit protein S was expressed in eucaryotic cells and found to be post-translationally modified, i.e. it had the correct amino terminus, contained N-linked carbohydrate side chains, gamma-carboxyglutamic acid residues and beta-hydroxylated aspartic acid and asparagine residues. Recombinant rabbit protein S bound calcium like its human counterpart, as judged by its migration in the presence of calcium on agarose-gel electrophoresis. Rabbit protein S has been reported to be species specific with respect to its interaction with APC and not to function with bovine APC. However, we found it to act as cofactor to both human and bovine APC, albeit it was somewhat more efficient with human than with bovine APC. Rabbit protein S, like its human and bovine counterparts, bound human C4BP in a reaction which was associated with the loss of its APC-cofactor activity. However, unlike human plasma, rabbit plasma appeared to contain only the free form of protein S as a radiolabeled rabbit protein S tracer added to rabbit plasma migrated as free protein S on agarose-gel electrophoresis. Addition of human C4BP to rabbit plasma resulted in the formation of a C4BP-protein-S complex, suggesting an explanation for the absence of complexed protein S in rabbit plasma to be sought for in the structure of rabbit C4BP.

We discuss some connections between the closure of a Steinberg fiber in the wonderful compactification of an adjoint group and the affine Deligne–Lusztig varieties X w (1) in the affine flag variety. Among other things, we describe the emptiness/nonemptiness pattern of X w (1) if the translation part of w is quasi-regular. As a by-product, we give a new proof of the explicit description of , first obtained in He [“Unipotent variety in the group compactification.” Advances in Mathematics 203 (2006): 109–31].

Affine Deligne-Lusztig varieties are analogs of Deligne-Lusztig varieties in the context of an affine root system. We prove a conjecture stated in the paper arXiv:0805.0045v4 by Haines, Kottwitz, Reuman, and the first named author, about the question which affine Deligne-Lusztig varieties (for a split group and a basic $\sigma$-conjugacy class) in the Iwahori case are non-empty. If the underlying algebraic group is a classical group and the chosen basic $\sigma$-conjugacy class is the class of $b=1$, we also prove the dimension formula predicted in op. cit. in almost all cases., Comment: 22 pages

Let H denote a spherical subgroup within a semisimple algebraic group G. In this paper we study the closures of the finitely many H-orbits in the flag variety of G. Using the language of Frobenius splitting we provide a criterion for these closures to have nice geometric and cohomological properties. We then show how the criterion applies to the spherical subgroups of minimal rank studied by N. Ressayre. Finally, we also provide applications of the criterion to orbit closures which are not multiplicity-free in the sense defined by M. Brion.

Let $G$ be a connected semi-simple algebraic group of adjoint type over an algebraically closed field, and let $\overline{G}$ be the wonderful compactification of $G$. For a fixed pair $(B, B^-)$ of opposite Borel subgroups of $G$, we look at intersections of Lusztig's $G$-stable pieces and the $B^-\times B$-orbits in $\overline{G}$, as well as intersections of $B \times B$-orbits and $B^- \times B^-$-orbits in $\overline{G}$. We give explicit conditions for such intersections to be non-empty, and in each case, we show that every non-empty intersection is smooth and irreducible, that the closure of the intersection is equal to the intersection of the closures, and that the non-empty intersections form a strongly admissible partition of $\overline{G}$.

Under suitable hypotheses, we prove that a form of a projective homogeneous variety $G/P$ defined over the function field of a surface over an algebraically closed field has a rational point. The method uses an algebro-geometric analogue of simple connectedness replacing the unit interval by the projective line. As a consequence, we complete the proof of Serre's Conjecture II in Galois cohomology for function fields over an algebraically closed field.

We study the minimal length elements in some double cosets of Coxeter groups and use them to study Lusztig's $G$-stable pieces and the generalization of $G$-stable pieces introduced by Lu and Yakimov. We also use them to study the minimal length elements in a conjugacy class of a finite Coxeter group and prove a conjecture in \cite{GKP}., Comment: 35 pages

By a case-free approach we give a precise description of the closure of a Steinberg fiber within a twisted wonderful compactification of a simple linear algebraic group. In the non-twisted case this description was earlier obtained by the first author., Comment: 12 pages, final version

The unipotent variety of a reductive algebraic group $G$ plays an important role in the representation theory. In this paper, we will consider the closure $\bar{\Cal U}$ of the unipotent variety in the De Concini-Procesi compactification $\bar{G}$ of a connected simple algebraic group $G$. We will prove that $\bar{\Cal U}-\Cal U$ is a union of some $G$-stable pieces introduced by Lusztig in \cite{L4}. This was first conjectured by Lusztig. We will also give an explicit description of $\bar{\Cal U}$. It turns out that similar results hold for the closure of any Steinberg fiber in $\bar{G}$., Comment: 21 pages. Final version. To appear in Adv. in Math

We study the nonnegative part \bar{G_{>0}} of the De Concini-Procesi compactification of a reductive algebraic group G, as defined by Lusztig. Using positivity properties of the canonical basis and parametrization of flag varieties, we will give an explicit description of \bar{G_{>0}}. This answers the question of Lusztig in [L4]. We will also prove that \bar{G_{>0}} has a cell decomposition which was conjectured by Lusztig., 23 pages. Some corrections. References updated

The nature of residue 225 on a consensus loop in serine proteases determines whether a protease can bind Na(+). Serine proteases with a Pro at this position are unable to bind Na(+), but those with a Tyr or Phe can bind Na(+). Factor Xa (FXa), the serine protease of the prothrombinase complex, contains a Tyr at this position. Na(+) is also known to stimulate the amidolytic activity of FXa toward cleavage of small synthetic substrates, but the role of Na(+) in the prothrombinase complex has not been investigated. In this study, we engineered a Gla-domainless form of FX (GDFX) in which residue Tyr(225) was replaced with a Pro. We found that Na(+) stimulated the cleavage rate of chromogenic substrates by FXa or GDFXa approximately 8-24-fold with apparent dissociation constants [K(d(app))] of 37 and 182 mM in the presence and absence of Ca(2+), respectively. In contrast, Na(+) minimally affected the cleavage rate of these substrates by the mutant, and no K(d(app)) for Na(+) binding to the mutant could be estimated. Unlike the wild-type enzyme, the reactivity of the mutant with antithrombin was independent of Na(+) and impaired approximately 32-fold. Ca(2+) improved the reactivity of the mutant with antithrombin approximately 5-fold. Affinity of the mutant for binding to factor Va was weakened and its ability to activate prothrombin was severely impaired. Further studies with the wild-type prothrombinase complex revealed that FXa binds to factor Va with a similar K(d(app)) of 1. 1-1.8 nM in the presence of Na(+), K(+), Li(+), Ch(+), and Tris(+) and that the catalytic efficiency of prothrombinase is enhanced less than 1.5-fold by the specific effect of Na(+) in the reaction buffer. These results suggest that (1) the loop including residue 225 (225-loop) is a Na(+) binding site in FXa, (2) the Na(+)- and Ca(2+)-binding loops of FXa are allosterically linked, and (3) the Tyr conformer of the 225-loop is critical for factor Xa function; however, both Na(+)-bound and Na(+)-free forms of factor Xa in the prothrombinase complex can efficiently activate prothrombin.

Thrombin undergoes allosteric modulation by thrombomodulin (TM) that results in a shift in macromolecular specificity, blocking fibrinogen clotting while enhancing protein C activation. The TM enhancement of protein C activation involves both an 8-fold decrease in Km and a 200-fold increase in kcat. Although TM-mediated conformational changes in thrombin have been detected by many techniques, the nature of these changes remains obscure. Access to the active center of thrombin is relatively restricted due to the presence of a large insertion loop at residue 60 (chymotrypsin numbering) that has been implicated in modeling studies as being responsible for poor inhibition by BPTI. Thrombin and the E192Q mutant, which binds BPTI much more tightly than thrombin, are both inhibited very slowly by BPTI. TM increases the rate of thrombin or thrombin E192Q inhibition by BPTI approximately 10-fold. When analyzed as slow tight binding inhibition, the TM effect on thrombin E192Q inhibition by BPTI is primarily on the first, reversible step in the reaction. Structural studies of the thrombin E192Q-BPTI complex have previously shown that the 60 loop lies over the BPTI, a position which requires 8 A movement at the apex of the 60 loop, and that BPTI is found in the same canonical orientation as in the trypsin complex. It follows that TM enhancement of the initial interaction of thrombin results in a conformation that favors interactions with BPTI, probably involving motion of the 60 loop.

Mutation of three Arg residues, 93, 97, and 101, to Ala in thrombin (thrombin R93,97,101A) has previously been shown to eliminate most heparin acceleration of thrombin inhibition by antithrombin and most of the ability of chondroitin sulfate (CS) on thrombomodulin (TM) to enhance affinity for TM and to eliminate the characteristic high-affinity interaction with protein C observed with TM lacking CS. In this study we examined the relative impact of mutation of these Arg residues alone and in combination on the above reactions and, in addition, on the ability of rabbit TM to accelerate thrombin inhibition by antithrombin. The order of importance for heparin acceleration of inhibition by antithrombin was Arg 101, 93, and 97. In contrast, Arg 97 was the major residue required for TM-dependent acceleration of reactivity with antithrombin and for CS-dependent enhancement of TM affinity. Arg 101 and 93 were critical for TM-dependent, high-affinity protein C interaction at low Ca2+ concentrations, while Arg 97, which was critical for the other TM-dependent effects, played no detectable role in this metal dependence. These results illustrate that these Arg residues in anion binding exosite 2 contribute very differently to the diverse reactions dependent on that domain in thrombin.

The interaction between vitamin K-dependent protein S and the C4b-binding protein (C4BP) was studied using surface plasmon resonance and genetic engineering. The affinity, as well as association and dissociation rates of the complex, was measured for human and bovine protein S at five different calcium concentrations. The binding to C4BP of six protein hybrids containing different parts of coagulation factor IX and protein S was studied in the absence and presence of calcium. The results show that dissociation of the human protein S-C4BP complex is extremely slow in the presence of > or = 10 microM calcium (k(off) = 7 x 10(-6) s(-1)) and the association rate constant is k(on) = 7 x 10(4) M(-1) s(-1). Human and bovine protein S were found to bind to human C4BP with the same affinity, K(D) = 0.1 nM, but the rates of association and dissociation were higher for the bovine protein S (k(on) = 2 x 10(5) M(-1) s(-1), k(off) = 2 x 10(-5) s(-1)). In the absence of calcium, the affinity for C4BP was reduced by a factor of 65 for human protein S and by a factor of 40 for bovine protein S. The decreased affinity could be mainly attributed to an increased off-rate (12-17-fold), while the on-rate decreased 3-4-fold. The studies using chimeric proteins show that the portion of protein S that is responsible for binding to C4BP is fully contained in the two laminin-G-type repeats, which are homologous to the sex hormone binding globulin (SHBG). All hybrids that contain the laminin-G-type repeats bind to C4BP with the same affinity as recombinant protein S, whereas hybrids lacking these repeats show no detectable binding to C4BP. The present data also suggest that the effect of calcium on the C4BP-binding properties is mediated by calcium binding site(s) in the laminin-G-type repeats.

Protein C is a vitamin K-dependent protein circulating in plasma as a zymogen to an anticoagulant serine protease. After its activation, protein C cleaves and inactivates coagulation factors Va and VIIIa. Human protein C is synthesized in liver and undergoes extensive post-translational modification during its synthesis. Recently, the protein C inhibitor was demonstrated to be synthesized in several organs of the human male reproductive tract. Moreover, vitamin K-dependent protein S, which functions as a co-factor to activated protein C, was found to be synthesized in the Leydig cells of human testis. The aim of this study was to elucidate whether the protein C gene is also expressed in the male reproductive system. Specific immunostaining of protein C was found in Leydig cells of human testis, in the excretory epithelium of epididymis, and in some epithelial glands of the prostate, whereas no immunostaining was detected in seminal vesicles. Northern blotting and non-radioactive in situ hybridization demonstrated protein C mRNA in Leydig cells, in the excretory epithelium of epididymis, and in some of the epithelial glands of the prostate. The mRNA was distributed perinuclearly and the localization was in accordance with the specific immunostaining for protein C. The epithelium of epididymis was also found to contain both protein S mRNA and immunoreactivity. The demonstration of both protein C and protein S immunoreactivities, as well as their mRNAs, in male reproductive tissues suggests as yet unknown local functions for these proteins.

Vitamin K-dependent protein S is an anticoagulant plasma protein that functions as a co-factor to activated protein C in the degradation of coagulation factors Va and VIIIa. We investigated the tissue/cellular distribution of protein S synthesis by Northern blotting, in situ hybridization, and immunohistochemistry. Northern blotting together with in situ hybridization, using specific oligodeoxynucleotide probes, demonstrated protein S mRNA in liver, lung, testis, epididymis, ovary, uterus, and brain. In the reproductive system, protein S mRNA was present in the cytoplasm of Leydig cells, interstitial cells of the ovary, epithelial cells of the epididymis, and in the endometrium, including endometrial mucous glandular membrane in the myometrium. Bronchial epithelial cells and alveolar macrophages were positive in the respiratory system. In the central nervous system, pyramidal neurons in the cerebral cortex and in the hippocampal region, and dentate fascia neurons gave strongly positive signals. Immunohistochemistry with monoclonal antibodies yielded a staining pattern that correlated well with results of in situ hybridization. In conclusion, results from Northern blotting, in situ hybridization, and immunohistochemistry suggested that rabbit protein S is expressed in several extrahepatic tissues. The presence of protein S transcripts in these fully differentiated cells suggests a cell type-specific gene expression which may be related to local anticoagulation or to other as yet unknown protein S functions.

SummaryHuman factor V has been shown not only to be a precursor to procoagulant factor Va but also to express anticoagulant properties. Thus, factor V was recently found to potentiate the effect of protein S as cofactor to activated protein C (APC) in the inactivation of the factor VIIIa-factor IXa complex. The purpose of this study was to determine whether the APC-cofactor function of factor V was also expressed in the bovine protein C system and to elucidate the molecular background for the species specificity of APC. For this purpose, the effects of protein S and factor V on APC-mediated inactivation of factor VIIIa were studied using purified APC, protein S and factor V of human and bovine.origin. The factor VIIIa investigated here was part of a Xase complex (i.e. factor IXa, factor VIIIa, phospholipid and calcium) and the APC-mediated inhibition of factor VIIIa was monitored by the ability of the Xase complex to activate factor X. Synergistic APC-cofactor function of factor V and protein S was demonstrated in the bovine system. The effect of bovine APC was potentiated by bovine protein S but not by human protein S, whereas both human or bovine protein S stimulated the function of human APC. Factor V did not express species specificity in its APC-cofactor activity even though bovine factor V was more potent than its human counterpart. Recombinant human/bovine protein S chimeras were used to demonstrate that the thrombin sensitive region and first epidermal growth factor-like module of protein S determine the species specificity of the APC-protein S interaction. In conclusion, both human and bovine factor V were found to express APC-cofactor activity which depends on the presence of protein S. The species specificity of APC was shown to be caused by the interaction between APC and protein S.

SummaryInherited resistance to activated protein C (APC) is a frequent cause of familial thrombosis. It is associated with a factor V gene point mutation replacing arginine506 in the APC-cleavage site with a glutamine. Thrombotic events are rare during childhood even in patients with homozygous APC-resistance. We now wish to report on a case of severe venous thrombosis, in a 10-year-old boy. He was found to have pronounced APC-resistance due to homozygous factor V gene mutation in combination with inherited type I protein S deficiency. The two traits were independently inherited in the family. The APC-resistance was partially corrected by adding factor V, whereas added protein S was without effect. This is the first reported case of homozygous APC-resistance combined with another inherited prothrombotic disorder. It illustrates how multiple genetic defects may provoke thrombosis at young age and emphasizes the need of complete evaluation of thrombotic patients in order to determine whether multiple risk factors exist.

SummaryIn human plasma, the anticoagulant vitamin K-dependent protein S exists in two molecular forms, as free protein and complexed to C4b- binding protein (C4BP), a complement regulatory protein. It has been suggested that rabbit plasma also contains two forms of protein S and that the interaction between protein S and C4BP m rabbits can be modulated by synthetic peptides corresponding to a sequence (residues 605-614) in the carboxy-lerminal part of protein S. In this report, we provide itsulls which challenge the conclusion that rabbit plasma contains the complexed form of protein S. The two forms of protein S in human plasma were separated by gel filtration chromatography on Sephacryl S-300 and the presence of protein S in the various fractions analyzed by Western blotting using a monoclonal antibody (HPS 21) directed against the γ-carboxyglutamic acid rich module of human protein S. This antibody, which was found to cross-react with rabbit protein S on Western blotting, was used in affinity purification of protein S from rabbit plasma as well as of recombinant rabbit protein S. HPS 21 specifically recognized protein S in rabbit plasma and did not cross-react with the other vitamin K-depeudenl plasma proteins. To elucidate whether rabbit plasma contained two forms of protein S, rabbit plasma was subjected to gelfiltration chromatography followed by Western blotting of the fractions with monoclonal antibody HPS 21. Protein S was found only in fractions eluting at a position corresponding to that of free protein S. A radiolabelled trace amount of recombinant rabbit protein S added to rabbit plasma chromatographed as free protein S and no high molecular weight form corresponding to a C4BP-protein S complex was detected. Rabbit protein S had the capacity to bind human C4BP and the addition of human C4BP to rabbit plasma changed the elution profile, of rabbit plasma protein S. After the addition of human C4BP, rabbit plasma protein S quantitatively eluted as a high molecular weight complex, suggesting that all the protein S in rabbit plasma was bound to human C4BP. The anticoagulant activity of human protein S is modulated by the complex formation with C4BP. Our results demonstrate that this function of C4BP and the protein S-C4BP complex formation has not been conserved throughout the evolution even though protein S has a preserved C4BP binding site.