Conantokin-GisaconopeptidethathasbeenisolatedfromthevenomoftheconeConusgeographus. Conantokin-Gselectivelyinhibits NR2B containingN-methyl-D-aspartatereceptors(NMDAR)withahighspecificity.Thus, Conantokin-G inhibitsinaconcentration-dependentmannertheCa2+ influxleADIngtoaneuroprotectiveeffectagainstNMDA-inducedexcitotoxicity. Conantokin-G wasshowntoblockNMDA-evokedcurrentsinmurinecorticalneuronswithanIC50 valueofaround480nM.
Description:
AAsequence: Gly-Glu-Gla-Gla-Leu-Gln-Gla-Asn-Gln-Gla-Leu-Ile-Arg-Gla-Lys-Ser-Asn-NH2
Length(aa): 17
Formula: C88H138N26O44
MolecularWeight: 2264.23Da
Appearance: Whitelyophilizedsolid
Solubility: waterandsalinebuffer
CASnumber: [93438-65-4]Source: Synthetic
Purityrate: >95%
Reference:
Opposingactionofconantokin-Gonsynapticallyandextrasynaptically-activatedNMDAreceptors
SynapticandextrasynapticactivationoftheN-methyl-D-aspartatereceptor(NMDAR)hasdistinctconsequencesoncellsignalingandneuronalsurvival.Sinceconantokin(con)-GantagonismisNR2B-selective,whichisthekeysubunitinvolvedinextrasynapticactivationofthereceptor,itsABIlitytospecificallyelicitdistinctsignalingoutcomesinneuronswithsynapticallyorextrasynaptically-activatedNMDARswasevaluated.InhibitionofCa(2+)influxthroughextrasynapticNMDARionchannelswasneuroprotective,asiteffectivelyenhancedlevelsofactivatedextracellularsignal-regulatedkinase1/2(ERK1/2),activatedcAMPresponseelementbindingprotein(CREB),enhancedmitochondrialviability,andattenuatedtheactindisorganizationobservedbyextrasynapticactivationofNMDARs.Conversely,thepro-signalingpathwaysstimulatedbysynaptically-inducedCa(2+)influxwereabolishedbycon-G.FurThermore,subunitnon-selectivecon-Twasunabletosuccessfullyredresstheimpairmentsinneuronscausedbyextrasynaptically-activatedNMDARs,thusindicatingthatNR2B-specificantagoNISTsarebeneficialforneuronsurvival.NeuronsablatedfortheNR2BsubunitshowedweaksynapticCa(2+)influx,reducedsensitivitytoMK-801blockage,anddiminishedextrasynapticcurrentcomparedtoWTandNR2A(-/-)neurons.ThisindicatesthattheNR2BsubunitisanintegralcomponentofbothsynapticandextrasynapticNMDARchannels.Altogether,thesedatasuggestthatcon-GspecificallytargetstheNR2Bsubunitinthesynapticandextrasynapticlocations,resultingintheopposingactionofcon-GondifferentiallyactivatedpoolsofNMDARs.
BalsaraR., etal. (2012)Opposingactionofconantokin-Gonsynapticallyandextrasynaptically-activatedNMDAreceptors.Neuropharmacology. PMID: 22306487
CGX-1007preventsexcitotoxiccelldeathviaactionsatmultipletypesofNMDAreceptors
Glutamateinducedexcitotoxicinjurythroughover-activationofN-methyl-D-aspartatereceptors(NMDARs)playsacriticalroleinthedevelopmentofmanyneurodegenerativediseases.ThepresentstudywasundertakentoevaluatetheroleofCGX-1007(ConantokinG)asaneuroprotectiveagentagainstNMDA-inducedexcitotoxicity.ConantokinG,aconesnailpeptideisolatedfromConusgeographusisreportedtoselectivelyinhibitNR2BcontainingNMDARswithhighspecificityandisshowntohavepotentanticonvulsantandantinociceptiveeffects.CGX-1007significantlyreducedtheexcitotoxiccelldeathinducedbyNMDAinorganotypichippocampalbrainsliceculturesinaconcentration-dependentmanner.Incontrast,ifenprodil,anotherNR2BspecificantagonistfailedtoofferneuroprotectionagainstNMDA-inducedexcitotoxicity.WefurtherdeterminedthattheneuroprotectionobservedislikelyduetotheactionofCGX-1007atmultipleNMDAreceptorsubtypes.Inaseriesofelectrophysiologyexperiments,CGX-1007inhibitedNMDA-gatedcurrentsinhumanembryonickidney(HEK)293cellsexpressingNMDAreceptorscontainingeitherNR1a/NR2BorNR1a/NR2Asubunitcombinations.CGX-1007producedaweakinhibitionatNR1a/NR2Creceptors,whereasithadnoeffectonNR1a/NR2Dreceptors.Further,theinhibitionofNMDAreceptorsbyCGX-1007wasvoltage-dependentwithgreaterinhibitionseenathyperpolarizedmembranepotentials.Thevoltage-dependenceofCGX-1007activitywasalsoobservedinrecordingsofNMDA-gatedcurrentsevokedinnativereceptorsexpressedincorticalneuronsinculture.Basedonourresults,weconcludethatCGX-1007isapotentneuroprotectiveagentthatactsasanantagonistatbothNR2AandNR2Bcontainingreceptors.
AlexAB., etal. (2011)CGX-1007preventsexcitotoxiccelldeathviaactionsatmultipletypesofNMDAreceptors.Neurotoxicology. PMID: 21396956
SpecificdeterminantsofconantokinsthatdictatetheirselectivityfortheNR2BsubunitofN-methyl-D-aspartatereceptors.
Conantokinsarenaturally-occurringsmallpeptideantagonistsofionflowthroughNMDA/glycineactivated-N-methyl-d-aspartatereceptor(NMDAR)ionchannels.Onememberoftheconantokinfamily,conantokin(con)-G,a17-residuepeptide,isselectiveforNMDARscontainingtheN-methyl-d-aspartatereceptorsubunit2B(NR2B),whereasthehomologouspeptides,con-Tandcon-R,showbroaderselectivityforNR2subunits.Inthisstudy,con-G,con-R,andcon-Tvariantswerechemicallysynthesizedandemployedtoinvestigatetheirsubunitselectivitiesasinhibitorsofagonist-evokedioncurrentsinhumanembryonickidney-293(HEK-293)cellsexpressingvariouscombinationsofNMDARsubunitsthatcontainNR1aorNR1bcombinedwithNR2AorNR2B.Usingtruncationandpointmutants,aswellaschimericconantokins,wedeterminedthattheN-terminusofcon-GcontainsallthedeterminantsforNR2Bselectivity.Withthisinformation,alargenumberof(con)variantsweresynthesizedandusedtoestablishminimalsequencedeterminantsforselectivity.Tyratposition5broadenstheNR2selectivity,andrecoveryofNR2BselectivityinTyr5peptideswasachievedbyincorporatingAlaorGlyatposition8.NR2Bselectivityincon-RcanbeconferredthroughdeletionoftheAlaatposition10,therebyshiftingtheγ-carboxyglutamate(Gla)fromposition11toposition10,whereaGlanaturallyoccursincon-Gandcon-T.Thenatureoftheaminoacidatposition6isalsolinkedtosubunitselectivity.OurstudiessuggestthatthemoleculardeterminantsofconantokinsthatdictateNMDARsubunitselectivityarehousedinspecificresiduesoftheN-terminiofthesepeptides.Thus,itispossIBLetoengineerdesiredNMDARfunctionalpropertiesintoconantokin-basedpeptides.
ShengZ., etal. (2010)SpecificdeterminantsofconantokinsthatdictatetheirselectivityfortheNR2BsubunitofN-methyl-D-aspartatereceptors. Neuroscience. PMID: 20688135
Theselectivityofconantokin-GforionchannelinhibitionofNR2Bsubunit-containingNMDAreceptorsisregulatedbyaminoacidresiduesintheS2regionofNR2B
Theconantokinsareshort,naturallyoccurringpeptidesthatinhibitionflowthroughN-methyl-d-aspartatereceptor(NMDAR)channels.Onememberofthispeptidefamily,conantokin-G(con-G),showshighselectivityforantagonismofNR2B-containingNMDARchannels,whereasotherknownconantokinsarelessselectiveinhibitorswithregardtothenatureoftheNR2subunitoftheNMDARcomplex.InordertodefinethemoleculardeterminantsofNR2Bthatgoverncon-Gselectivity,weevaluatedtheabilityofcon-GtoinhibitNMDARionchannelsexpressedinhumanembryonickidney(HEK)293cellstransfectedwithNR1,incombinationwithvariousNR2A/2Bchimerasandpointmutants,byelectrophysiologyusingcellsvoltage-clampedinthewhole-cellconfiguration.Wefoundthatavariantofthecon-G-insensitivesubunit,NR2A,inwhichthe158residuescomprisingtheS2peptidesegment(E(657)-I(814))werereplacedbythecorrespondingS2regionofNR2B(E(658)-I(815)),resultsinreceptorsthatarehighlysensitivetoinhibitionbycon-G.Ofthe22aminoacidsthataredifferentbetweentheNR2A-S2andtheNR2B-S2regions,exchangeofoneofthese,M(739)ofNR2BfortheequivalentK(738)ofNR2A,wassufficienttocompletelyimporttheinhibitoryactivityofcon-GintoNR1b/NR2A-containingNMDARs.Somereinforcementofthiseffectwasfoundbysubstitutionofasecondaminoacid,K(755)ofNR2BforY(754)ofNR2A.ThediscoveryofthemoleculardeterminantsofNR2Bselectivitywithcon-Ghasimplicationsforthedesignofsubunit-selectiveneuroBIOLOGicalprobesanddrugtherapies,inadditiontoadvancingourunderstandingofNR2B-versusNR2A-mediatedneurologicalprocesses.
ShengZ., etal.(2009)Theselectivityofconantokin-GforionchannelinhibitionofNR2Bsubunit-containingNMDAreceptorsisregulatedbyaminoacidresiduesintheS2regionofNR2B. Neuropharmacology. PMID: 19427876
Powerfulantinociceptiveeffectsoftheconesnailvenom-derivedsubtype-selectiveNMDAreceptorantagonistsconantokinsGandT
Subunitnon-selectiveN-methyl-D-aspartate(NMDA)receptorantagonistsreduceinjury-inducedpainbehavior,butgenerallyproduceunacceptablesideeffects.Inthisstudy,weexaminedtheantinociceptiveandmotoreffectsofconesnailvenom-derivedpeptides,conantokinsGandT(conGandconT),whichareselectiveinhibitorsoftheNR2BorNR2AandNR2BsubtypesoftheNMDAreceptor,respectively.WetestedtheeffectsofconGandconTinmodelsoftissue(formalintest),nerveinjury(partialsciaticnerveligation)andinflammation-induced(intraplantarCompleteFreund’sAdjuvant;CFA)paininmice.Intheformalintest,intrathecal(i.t.)conGorconTsuppressedtheongoingpainbehavior(ED(50)and95%confidenceintervals(CI),11(7-19)and19(11-33),respectively)atdosesthatwere17-27timeslowerthanthoserequiredtoimpairmotorfunction(acceleratingrotarodtreadmilltest:ED(50)and95%CI,300(120-730)and320(190-540)pmol,respectively).Bycomparison,SNX-111,anN-typevoltage-sensitivecalciumchannelantagonistthatisalsoderivedfromconesnailvenom,producedsignificantmotorimpairmentatadose(3.0pmol,i.t.)thatwasonlypartiallyefficaciousintheformalintest.Furthermore,conGreversedtheallodyniaproducedbynerveinjury,withgreaterpotencyonthermal(ED50and95%CI,24(10-55)pmol)thanonmechanicalallodynia(59(33-105)pmol).Finally,asingledoseofconG(100pmol,i.t.)alsoreducedCFA-evokedthermalandmechanicalallodynia.Takentogether,theseresultsdemonstratethatconantokinsexhibitpotentantinociceptiveeffectsinseveralmodelsofinjury-inducedpain.ThestudysupportsthenotionthatdrugsdirectedagainstsubtypesoftheNMDAreceptor,byvirtueoftheirreducedside-effectprofile,holdpromiseasnoveltherapeuticagentsforthecontrolofpain.
Malmberg,AB., etal.(2003)Powerfulantinociceptiveeffectsoftheconesnailvenom-derivedsubtype-selectiveNMDAreceptorantagonistsconantokinsGandT, Pain. PMID: 12507705
Theaminoacidresidueatsequenceposition5intheconantokinpeptidespartiallygovernssubunit-selectiveantagonismofrecombinantN-methyl-D-aspartatereceptors
Wholecellvoltageclamprecordingswereperformedtoassesstheabilityof conantokin-G(con-G), conantokin-T(con-T),anda17-residue truncatedformof conantokin-R(con-R[1-17])toinhibit N-methyl-d-aspartate (NMDA)-evokedcurrentsinhumanembryonickidney293cellstransientlyexpressingvariouscombinationsofNR1a,NR1b,NR2A,andNR2Breceptorsubunits.Con-Tandcon-R[1-17]attenuatedioncurrentsincellsexpressingNR1a/NR2AorNR1a/NR2B.Con-GdidnotaffectNMDA-evokedioniccurrentsincellsexpressingNR1a/NR2A,butitshowedinhibitoryactivityincellsexpressingNR1a/NR2B receptors andthetriheteromericcombinationofNR1a/NR2A/NR2B.AnAla-richcon-Ganalog,con-G[Q6G/gamma7K/N8A/gamma10A/gamma14A/K15A/S16A/N17A](Ala/con-G,wheregammaisGla),inwhichallnonessential amino acidswerealteredtoAlaresidues,manifestedsubunitspecificitysimilartothatofcon-G,suggestingthatthereplacedresiduesarenotresponsibleforselectivityinthecon-Gframework.Asarcosine-containingcon-Ttruncationanalog,con-T[1-9/G1Src/Q6G],inhibitedcurrentsinNR1a/NR2AandNR1a/NR2Breceptors,eliminatingresidues10-21asmediatorsofthebroadsubunitselectivityofcon-T.Incontrasttothenulleffectsofcon-GandAla/con-GataNR1a/NR2A-containingreceptor,someinhibition(approximately40%)ofNMDA-evokedcurrentswaseffectedbythese peptides incellsexpressingNR1b/NR2A.Thisfindingsuggeststhatthepresenceofexon 5 inNR1bplaysaroleintheactivityoftheconantokins.Analysisofvarious conantokinanalogsdemonstratedthatLeu(5)ofcon-Gisanimportantdeterminantof conantokin selectivity.Takenasawhole,theseresultssuggestthattheimportantmoleculardeterminantsonconantokinsresponsibleforNMDAreceptoractivityandspecificityarediscretelyhousedinspecificresiduesofthese peptides,thusallowingmolecularmanipulationoftheNMDAreceptorinhibitorypropertiesoftheconantokins.
Klein,R.C.,etal.(2001)Theaminoacidresidueatsequenceposition5intheconantokinpeptidespartiallygovernssubunit-selectiveantagonismofrecombinantN-methyl-D-aspartatereceptors, JBiolChem.PMID: 11335724
ConantokinGisanNR2B-selectivecompetitiveantagonistofN-methyl-D-aspartatereceptors.
ConantokinG(ConG)isa17-amino-acidpeptideantagonistofN-methyl-D-aspartate(NMDA)receptorsisolatedfromthevenomofthemarineconesnail,Conusgeographus.ThemechanismofactionofConGhasnotbeenwelldefined;bothcompetitiveandnoncompetitiveinteractionswiththeNMDA-bindingsitehavebeenproposed.InthisstudythemechanismofactionandsubunitselectivityofConGwasexaminedinwhole-cellvoltage-clamprecordingsfromculturedneuronsandintwoelectrodevoltage-clamprecordingsfromXenopusoocytesexpressingrecombinantNMDAreceptors.ConGwasapotentandselectiveantagonistofNMDA-evokedcurrentsinmurinecorticalneurons(IC(50)=480nM).TheslowonsetofConGblockcouldbepreventedbycoapplicationwithhighconcentrationsofNMDAorofthecompetitiveantagonist(RS)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonicacid.Furthermore,inoocytesexpressingNR1a/NR2Breceptors,ConGproducedarightwardshiftintheconcentration-responsecurveforNMDA,providingsupportforacompetitiveinteractionwiththeNMDA-bindingsite.ConGproducedanapparentnoncompetitiveshiftintheconcentration-responsecurveforsperminepotentiationofNMDAresponses,butthiswasduetospermine-inducedenhancementofConGblock.SpermineproducedasimilarenhancementofDL-2-amino-S-phosphopentanoicacidblock.Finally,ConGselectivelyblockedNMDAreceptorscontainingtheNR2Bsubunit.TheseresultsdemonstratethatConGisasubunit-specificcompetitiveantagonistofNMDAreceptors.TheuniquesubunitselectivityprofileofConGmayexplainitsfavorableinvivoprofilecomparedwithnonselectiveNMDAantagonists.
DonevanSD., etal. (2000)ConantokinGisanNR2B-selectivecompetitiveantagonistofN-methyl-D-aspartatereceptors. MolPharmacol. PMID: 10953056
Bindingofcationstoindividualgamma-carboxyglutamateresiduesofconantokin-Gandconantokin-T
Conantokin-G(con-G)andconantokin-T(con-T)arenaturallyoccurringgamma-carboxyglutamate(Gla)-containingpeptidesthatinteractwithmultivalentcationsinfunctionallyrelevantmanners.Selective13C-enrichmentofCgammaandCdeltaineachoftheGlaresidueshasallowedmetalbindingaffinitiestobemeasuredatindividualsidechains.Con-Tpossessestwometalbindingsites,onewithhighaffinityatGla10/Gla14andanotherwithweakbindingatGla3/Gla4.Con-GcontainstwositesofcomparablelowaffinityforCa2+.Analysisofthe13Cline-widthsofcon-GinthepresenceofMg2+allowedtheorderofmetalbindingtobedetermined,withGla10/Gla14loadingbeforetheGla3/Gla4/Gla7cluster.Whilethevariantpeptide,apo-con-T[Lys7Gla],wasshowntohaveaverylowalpha-helicalcontent,thispeptidebindsasecondmetalwithmuchgreateraffinitythanwild-typecon-T.ThisprovidesadditionalevidencethatGla7incon-Gisprimarilyresponsiblefordestabilizingtheapo-form,butisanimportantligandformetalchelation.Theresidue-specificalpha-helicalstabilitiesofcon-Gandcon-Tintheirmetal-freeandmetal-loadedstateswereestimatedbydeterminingratesofprotonexchangefrombackbonepeptidebondamideswithdeuteriumatomsfrom2H20-containingsolvents.Forbothpeptides,thelifetimesofprotonsonseveralpeptidebondamidesincreasedasmetalsofhigheraffinitywereboundtothepeptides,withthelongesthalf-livesfoundintheregionofthealpha-helicalturnstabilizedbytheGla10/Gla14metalcoordinationsite.WeproposethatGla10andGla14constitutetheprimarytightmetalionbindingsiteinbothpeptides.Thisdetailedanalysiswithphysiologicallyrelevantmetalcationsiscrucialfordecipheringtherolesofcriticalaminoacidsinthebioactivityoftheconantokinpeptides.
Blandl,T., etal.(1999)Bindingofcationstoindividualgamma-carboxyglutamateresiduesofconantokin-Gandconantokin-T, JPeptRes. PMID: 10406223
NMDA-receptorantagonistrequirementsinconantokin-G.
Aseriesofvariantsoftheneuroactive17-residuegamma-carboxyglutamate-(Gla)-containingpolypeptide,conantokin-G(con-G),weresynthesizedwiththeintentionofdeterminingthosefeaturesthatwereimportantforitsN-methyl-D-aspartate(NMDA)receptor-targetedantagonistactivityandforadoptionofitsdivalentcation-dependentalpha-helicalconformation.Employingthebindingof[3H]dizolcipine(MK-801)asanassayforopenreceptorionchannelsinratbrainmembranes,whichdisplaysinhibitionbycon-G(IC50=0.48microM),itwasfoundthatreplacementbyanAlaresidueofGla4ledtocompleteinactivationofthepeptide,whereasasimilarreplacementofGla3resultedina20-folddecreasedpotency.AlasubstitutionsforGla10andGla14didnotsubstantiallyaffect[3H]MK-801binding.ThissamesubstitutionatGla7appearedtoslightlyenhancebinding.Alareplacementsofnon-Glaresiduesdemonstratedthatfourofthem,viz.Glu2,Leu5,Gln9,andIle12,possessedatleast200-folddecreasesininhibitorypotency,whereassimilarreplacementsatGly1,Leu11,andArg13resultedinpeptideswith8-to12-foldincreasesintheIC50values.TheremainingaminoacidresiduestestedinthesingleAlareplacementseriesshowednosignificantchangesintheinhibitorycharacteristicsofwild-typecon-G.Additionalstudieswithcarboxyl-terminaltruncatedpeptidesrevealedthatthecarboxyl-terminal4aminoacidswereunimportantforthisactivity.Therewasnostrictcorrelationofinhibitionof[3H]MK-801bindingwiththeabilityofthesepeptidestoformcation-dependentalpha-helices.Peptideswithnotablylowalpha-helicalcontentinthepresenceofthesecationswerelackingatleastone,orboth,ofGla10andGla14.Con-G[Gla3,4,7,10,14E]andcon-G[Gla7,10,14E]weretheonlypeptidesthatremainedinacompletelyrandomconformationuponmetalionaddition.
BlandlT., etal. (1998)NMDA-receptorantagonistrequirementsinconantokin-G. FEBSLett. PMID: 9762921
Conantokin-G:anovelpeptideantagonisttotheN-methyl-D-asparticacid(NMDA)receptor
Conantokin-Gisa17aminoacidpeptideisolatedfromthevenomofthefish-eatingsnailConusgeographuswhichproduceshyperactivitywheninjectedintothebrainsofadultmice.WeshowthatthispeptideisaselectiveN-methyl-D-aspartate(NMDA)antagonistbasedonitsabilitytoblockNMDA-inducedelevationofcGMPinratcerebellarslicesinvitro(IC50=171nM),butnotkainicacid-inducedelevations.ThisinhibitioncouldnotbeovercomebyincreasingtheNMDAconcentration,indicatingnon-competitiveinhibition.Conantokin-Gdisplayednoaffinityforbindingsitesforthienylcyclohexylpiperidine,variousglutamatesubclassesorthoseforseveralotherneurotransmitters/neuromodulators.Thispeptide,however,enhanced[3H]glycinebindingtoratforebrainmembranesbutnottospinalcordmembranes.Theactivityprofileofthepeptideinvariousassaysindicatesthatitisanoveltypeofnon-competitiveNMDAantagonist.
MenaEE.,etal.(1990)Conantokin-G:anovelpeptideantagonisttotheN-methyl-D-asparticacid(NMDA)receptor.NeurosciLett. PMID: 2177176
ebiomall.com
>
>
>
>
>
>
>
>
>
>
>
>
pH(1)=pKa+lg[c(CH₃COONa)/c(CH₃COOH)]=pKa=4.74
通HCl后,溶液是c(CH₃COOH)=0.2mol/L、c(NaCl)=0.1mol/L的混合溶液,溶液pH按照弱酸溶液pH的求法求.
c(H⁺)=√[Ka*c(CH₃COOH)]=√(10^-4.74*0.2)=0.00191(mol/L)（采用了近似公式）
pH(2)=-lg{c(H⁺)}=2.72
两个pH求得,那么pH的变化量也就可得了.pH的变化量=|pH(2)-pH(1)|=|2.72-4.74|=2.02
1）PH缓冲溶液作用原理和pH值
当往某些溶液中加入一定量的酸和碱时,有阻碍溶液pH变化的作用,称为缓冲作用,这样的溶液叫做缓冲溶液.弱酸及其盐的混合溶液（如HAc与NaAc）,弱碱及其盐的混合溶液（如NH3·H2O与NH4Cl）等都是缓冲溶液.
由弱酸HA及其盐NaA所组成的缓冲溶液对酸的缓冲作用,是由于溶液中存在足够量的碱A-的缘故.当向这种溶液中加入一定量的强酸时,H离子基本上被A-离子消耗：
所以溶液的pH值几乎不变；当加入一定量强碱时,溶液中存在的弱酸HA消耗OH-离子而阻碍pH的变化.
2）PH缓冲溶液的缓冲能力
在缓冲溶液中加入少量强酸或强碱,其溶液pH值变化不大,但若加入酸,碱的量多时,缓冲溶液就失去了它的缓冲作用.这说明它的缓冲能力是有一定限度的.
缓冲溶液的缓冲能力与组成缓冲溶液的组分浓度有关.0.1mol·L-1HAc和0.1mol·L-1NaAc组成的缓冲溶液,比0.01mol·L-1HAc和0.01mol·L-1NaAc的缓冲溶液缓冲能力大.关于这一点通过计算便可证实.但缓冲溶液组分的浓度不能太大,否则,不能忽视离子间的作用.
组成缓冲溶液的两组分的比值不为1∶1时,缓冲作用减小,缓冲能力降低,当c（盐）/c（酸）为1∶1时△pH最小,缓冲能力大.不论对于酸或碱都有较大的缓冲作用.缓冲溶液的pH值可用下式计算：
此时缓冲能力大.缓冲组分的比值离1∶1愈远,缓冲能力愈小,甚至不能起缓冲作用.对于任何缓冲体系,存在有效缓冲范围,这个范围大致在pKaφ（或pKbφ）两侧各一个pH单位之内.
弱酸及其盐（弱酸及其共轭碱）体系pH=pKaφ±1
弱碱及其盐（弱碱及其共轭酸）体系pOH=pKbφ±1
例如HAc的pKaφ为4.76,所以用HAc和NaAc适宜于配制pH为3.76～5.76的缓冲溶液,在这个范围内有较大的缓冲作用.配制pH=4.76的缓冲溶液时缓冲能力最大,此时（c（HAc）/c（NaAc）=1.
3）PH缓冲溶液的配制和应用
为了配制一定pH的缓冲溶液,首先选定一个弱酸,它的pKaφ尽可能接近所需配制的缓冲溶液的pH值,然后计算酸与碱的浓度比,根据此浓度比便可配制所需缓冲溶液.
以上主要以弱酸及其盐组成的缓冲溶液为例说明它的作用原理、pH计算和配制方法.对于弱碱及其盐组成的缓冲溶液可采用相同的方法.
PH缓冲溶液在物质分离和成分分析等方面应用广泛,如鉴定Mg2离子时,可用下面的反应：
白色磷酸铵镁沉淀溶于酸,故反应需在碱性溶液中进行,但碱性太强,可能生成白色Mg（OH）2沉淀,所以反应的pH值需控制在一定范围内,因此利用NH3·H2O和NH4Cl组成的缓冲溶液,保持溶液的pH值条件下,进行上述反应.
:)
我在做一细菌不同酸碱度生长状况时,发现这些奇怪现象:pH=3的培养基灭菌(TSB液体培养基)灭菌后pH上升到到9.2!而原来pH=9.0的降到8.7(基本没多少变化),请问各位大侠,这是什么原因?
一般做不同酸碱度生长实验时,该如何才能防止pH在湿热灭菌后基本不变化?
1.直接用固体磷酸钠配制成50mM的磷酸钠溶液，再调pH到7.4；（我们试着用这个做了下，发现挂不上柱）
2.配置磷酸钠盐缓冲液：按NaH2PO4：Na2HPO4以19：81的摩尔比配制成pH7.4的缓冲液？（附一张百度出来的配方
）
3.如果是磷酸钠盐缓冲液，可以直接将50mM的NaH2PO4的水溶液用NaOH调成pH7.4吗？
再者，2和3这两个方法配制的磷酸钠盐缓冲液有什么区别？最终效果是一样的吗？如果不一样，有什么理论的知识支撑呢？个人感觉是分析化学中酸碱理论中的缓冲液那里的知识。求帮忙解答这些疑问。
另外，我还想问一下，pH对于Ni柱对His-tagged的蛋白的分离纯化影响大吗？是怎么影响的？谢谢大家了！
两个CEX方法A和B测定同一单抗，结果碱性峰比例差不多，酸性峰比例相差约7%，相应主峰也差了7%左右。
具体来说，A方法酸性峰高，主峰低，碱性峰稍微低点；B方法酸性峰低，主峰高，碱性峰稍微高点；另外也做了CIEF，结果呢和A方法更接近。
仔细比较起来，AB两个方法的峰性和数量差不多，就不知道为什么会有这么大的差异。两个方法一个用的WCX柱-磷酸缓冲液，一个用SCX柱-MES缓冲液
大家帮我分析下：
1.两个方法哪个方法更准确，是以酸性峰高的为准还是什么？为什么？
2.这显著差异是由方法造成，具体原因是什么？柱子？
3.CIEF的结果和A方法更接近，是不是可以由此证明A方法更好或者CIEF的方法更好（因为CIEF更快更方便）？
欢迎讨论~
纠正下，A方法用的是Tosoh的柱子，B方法用的是SCX柱。TOSOH的柱子是7um的填料，10cm长。SCX是10um的填料。我本人TOSOH的阳离子柱子用的很少，这次信手用用，结果发现差异很大
那我现在就考虑，在以后方法开发过程中，除了通过流动相pH和组成、梯度、柱子选择来获得样品主峰和酸碱性的最大分离，还要关注各峰比例。因为之前比较方法好坏都只看分离度，尤其是主峰和邻近峰的分离度，获得最大分离度，自然可以做到主峰尽可能纯，但从未认真比较过各峰比例。这是一个大疏忽吧！
另外，CIEF和CEX方法原理还是有点差异的，所以分的是不同的异质体，原液放行两个方法肯定是都要做的。问题就是在早期细胞株筛选和工艺开发阶段，哪个方法才是又快又准。CIEF（iCE280)一般15分钟一个样，比CEX快多了。如果CIEF测得主峰要低于CEX结果，是不是真的完全可以取代CEX呢？CEX分离出的峰远比CIEF的多！
欢迎大家继续讨论~
因为是考察不同PH对药物的影响，样品又不好改变其PH值，这种情况怎么办？希望有经验的高手指教。
我的流动相是甲醇-水（90：10）
谢谢赐教！
请进子版按格式发贴，自行修改，谢谢。
这就是说不用酸碱预处理吗？
Whatman的网站上没有DE52最大耐受压力，请问又经验的战友应该是多少？
Whatman的网站上：
DE32DryMicrogranularDEAECellulose
SimilarperformancecharacteristicsafterprecyclingasDE52.
DE52PreswollenMicrogranularDEAECellulose
ProbablythemostwidelyusedDEAEcelluloseintheworld;usedforbiopolymerswithlowtohighnegativecharges;exhibitsexcellentresolutionwithgoodflowrates.
附件是一本图书(MethodsinMolecularMedicine,)的章节,上面说:
WhatmanDEAE52comesalreadypreswollenandonlyneedstobetransferred
totherunningbuffer50mMTE8.
lAntibodiesUsingIonExchangeChromatography.pdf(87.06k)
暂无品牌分类
© 2005- 苏州蚂蚁淘生物科技有限公司 版权所有。
苏ICP备17049038号-11
苏公网安备 32059002001627号
声明：本网站部分产品受外界条件影响（包含但不限于进口国出口国政策限制等因素），无法提供销售服务，下单后，会由客服人员联系厂家确认后另行通知。部分危险品无法清关，请勿下单
我要提问
您的问题将推送给已购用户，TA们将会为你解答。