| Formulation | 25mMHepes,2MNaCl,pH7.4 |
| Storage | -80°C |
| Purity | >95%bySDS-PAGE |
| ActivityDetermination | Heparinneutralization |
| ShelfLife(properlystored) | 12months |
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DomainStructureofPlateletFactor4Thedomainstructureoftheplateletfactor-4monomerisrepresented.Theplateletfactor-4monomerisa7,800molecularweightpeptide.Theheparin-bindingdomainispresumablylocalizedwithinaCOOH-terminalregionofthemoleculewhereseverallysineresiduesareclustered.Initsnativestate,plateletfactor-4isahomotetramerwhichexistsincomplexwithahighmolecularweightproteoglycancarrierprotein.
SampleGelInformation:
| Load | HumanPlateletFactor4,1µgperlane |
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| Buffer | MOPS |
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| Standard | SeeBluePlus2;Myosin(191kDa),PhosphorylaseB(97kDa),BSA(64kDa),GlutamicDehydrogenase(51kDa),AlcoholDehydrogenase(39kDa),CarbonicAnhydrase(28kDa),MyoglobinRed(19kDa),Lysozyme(14kDa) |
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Overview:
Plateletfactor-4(PF-4)isalowmolecularweight,heparin-bindingproteinwhichissecretedfromagoNIST-activatedplatelets(1,2).PF-4islocalizedwithintheplateleta-granule(2)whereitsconcentrationrangesfrom11.2-12.4µgper109plateletsmakingit,onamolarbasis,oneofthemostabundantproteinsintheplatelet(1,2).SincetherelativeconcentrationofPF-4inplateletsexceedsthatofplasmaby280,000-fold(3),PF-4levelsinplasmahavebeenutilizedasameasureofplateletactivationinvivo.PF-4issecretedfromplateletsincomplexwithahighmolecularweight,proteoglycan,carrierprotein(4,5).Sedimentationequilibriumexperimentshaveshownthatintheabsenceofitsproteoglycancarrier,themolecularweightofPF-4is27,000-29,000(4,5).SubsequentaminoacidsequencingofPF-4revealedamolecularweightof7,800(6-8)indicatingthatnativePF-4isahomotetramer.Functionally,PF-4neutralizestheanticoagulantactivityofheparininplasma.TheheparinbindingsitewithinPF-4ispresumablylocatedwithinthelysine-rich,COOH-terminalregionofthemolecule(6-8).Sincesolubleheparinisatherapeuticagent,thephysiologicalsignificanceoftheanti-heparinactivityofPF-4isnotknown.However,byinteractingwithcellsurfaceexpressedheparin-likeglycosaminoglycansonendothelialcells,PF-4mayexertitsprocoagulanteffect(9,10).PF-4bindingtocellsurfaceglycosaminoglycansmayalsobeamechanismthroughwhichPF-4stimulatesthereleaseofhistaminefrombasophils(11).ThechemotacticactivityofPF-4towardneutrophilsandmonocytes(12)hasalsobeenlocalizedtotheCOOH-terminal,presumedheparin-bindingdomainofPF-4(13).WhilePF-4isprimarilyasecretedprotein,PF-4bindingsitesontheplateletsurfacehavebeenidentifiedwhichmaybeimportantforplateletaggregation(14).
HumanPF-4ispreparedfromthesupernatantofthrombin-activatedplateletsbyheparin-agaroseaffinitychromatography(15).Thepurifiedproteinissuppliedin25mMHepespH7.4,2MNaClandshouldbestoredat-80oC.PurityisassessedbySDS-PAGEanalysisandheparin-neutralizingactivityisverifiedbyclottingassay.
Properties:
| Localization | plateleta-granule(2) |
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| Modeofaction | neutralizestheanticoagulantactivityofheparin.PlasmaconcentrationisusedasaMarkerofplateletactivation. |
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| Molecularweight | 29,000(4) |
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| Extinctioncoefficient | | E | | =2.6-calculatedbaseduponaminoacidsequenceandmolecularweight |
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| Isoelectricpoint | 7.6(16) |
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| Structure | homotetramer(monomer,Mr~7800)(5-7) |
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