SNX-482 hasbeenisolatedfromthevenomoftheSpiderHysterocratesgigas(Africantarantula). SNX-482 modulatestheR-type currentassociatedwiththeclassα1Ecalciumchannel(Cav2.3 fromtheCACNA1Egene). SNX-482 antagonizeschannelactivationbyinducingadepolarizingshiftintheactivationpotential,thuspreventingthechannelfromundergoingnormalmembranedepolarization. SNX-482 actsrapidlyandmaintainsitseffect.
Description:
AAsequence: Gly-Val-Asp-Lys-Ala-Gly-Cys7-Arg-Tyr-Met-Phe-Gly-Gly-Cys14-Ser-Val-Asn-Asp-Asp-Cys20-Cys21-Pro-Arg-Leu-Gly-Cys26-His-Ser-Leu-Phe-Ser-Tyr-Cys33-Ala-Trp-Asp-Leu-Thr-Phe-Ser-Asp-OH
Disulfidebonds: Cys7-Cys21,Cys14-Cys26 andCys20-Cys33
Length(aa): 41
Formula: C192H274N52O60S7
MolecularWeight: 4496.42Da
Appearance:Whitelyophilizedsolid
Solubility: waterandsalinebuffer
CASnumber: 203460-30-4
Source: Synthetic
Purityrate: >95%
Reference:
TheCav2.3calciumchannelantagoNISTSNX-482reducesdorsalhornneuronalresponsesinaratmodelofchronicneuropathicpain
Neuropathicpainisadifficultstatetotreat,characterizedbyalterationsinsensoryprocessingthatcanincludeallodynia(touch-evokedpain).Evidenceexistsfornervedamage-inducedplasticityinbothtransmission&modulatorysystems,includingchangesinvoltage-dependentcalciumchannel(VDCC)expression&function;however,theroleofCa(v)2.3calciumchannelshasnotclearlybeendefined.Here,theeffectsofSNX-482,aselectiveCa(v)2.3antagonist,onsensorytransmissionatthespinalcordlevelhavebeeninvestigatedintherat.Thespinalnerveligation(SNL)modelofchronicneuropathicpain[Kim&Chung,(1992)Pain,50,355-363]wasusedtoinducemechanicalallodynia,astestedontheipsilateralhindpaw.Invivoelectrophysiologicalmeasurementsofdorsalhornneuronalresponsestoinnocuous&noxiouselectricalandnaturalstimuliweremadeafterSNL&comparedtosham-operatedanimals.SpinalSNX-482(0.5-4microg/50microL)exerteddose-relatedinhibitionsofnoxiousC-fibre-andAdelta-fibre-mediatedneuronalresponsesinconditionsofneuropathy,butnotinsham-operatedanimals.MeasuresofspinalcordhyperexcitABIlity&nociceptionweremostsusceptIBLetoSNX-482.Incontrast,non-noxiousAbeta-mediatedresponseswerenotaffectedbySNX-482.Moreover,responsestoinnocuousmechanical&alsothermalstimuliweremoresensitivetoSNX-482inSNLthancontrolanimals.ThisstudyisthefirsttodemonstrateanantinociceptiveroleforSNX-482-sensitivechannelsindorsalhornneuronsduringneuropathy.ThesedataareconsistentwithplasticityinCa(V)2.3calciumchannelexpressionandsuggestapotentialselectivetargettoreducenociceptivetransmissionduringconditionsofnervedamage.
MatthewsEA., etal.(2007)TheCav2.3calciumchannelantagonistSNX-482reducesdorsalhornneuronalresponsesinaratmodelofchronicneuropathicpain. EurJNeurosci. PMID17610575
SNX482selectivelyblocksP/QCa2+channelsanddelaystheinactivationofNa+channelsofchromaffincells
TheeffectsofthetoxinSXN482onCa2+channelcurrents(ICa),Na+currents(INa),andK+currents(IK)havebeenstudiedinbovineadrenalmedullarychromaffincellsvoltage-clampedat-80mV.Currentswereelicitedbydepolarisingpulsesto0-10mV(ICaandINa)orto+60mV(IK).SNX482blockedICainaconcentration-dependentmanner.Theinhibitioncurveexhibitedtwophases.Thefirsthigh-affinityphasecomprised28%ofthewhole-cellcurrent&exhibitedanIC50of30.2nM.Thesecondlow-affinityphasecomprisedover70%ofICa&hadanIC50of758.6nM.Blockadewasrapidandfullyreversibleuponwashoutofthetoxin.OcclusionexperimentsshowedadditivityofblockadeexertedbynifedipineplusSNX482(0.3microM)andbyomega-conotoxinGVIAplusSNX482.Incontrast,blockadeexertedbycombinedomega-agatoxinIVAplusSNX482(about50%ofthewholecell)didnotshowadditivity.At0.3microMandhigherconcentrations,SNX482delayedtheinactivationofINa.Thetimeconstant(tau)forinactivationofINaincontrolconditionsdoubledinthepresenceof0.5microMSNX482.At0.3microM,SNX482didnotaffectIK.Ourdatademonstratethat:(i)SNX482selectivelyblocksP/QCa2+channelsatsubmicromolarconcentrations;(ii)thetoxinpartiallyblocksNa+channels;(iii)SNX482delaystheinactivationofNa+channels.TheseresultsrevealnovelpropertiesofSNX482andcastdoubtsontheclaimedselectivity&specificityofthetoxintoblocktheR-typeCa2+channel.
ArroyoG, etal.(2003)SNX482selectivelyblocksP/QCa2+channelsanddelaystheinactivationofNa+channelsofchromaffincells, EurJPharmacol. PMID:12954354
InteractionofSNX482withdomainsIIIandIVinhibitsactivationgatingofalpha(1E)(Ca(V)2.3)calciumchannels
Bourinet,E., etal. (2001)InteractionofSNX482withdomainsIIIandIVinhibitsactivationgatingofalpha(1E)(Ca(V)2.3)calciumchannels, Biophys. PMID11423396
SelectivepeptideantagonistoftheclassEcalciumchannelfromthevenomofthetarantulaHysterocratesgigas
WedescribethefirstpotentandselectiveblockeroftheclassECa2+channel.SNX-482,anovel41aminoacidpeptidepresentinthevenomoftheAfricantarantula,Hysterocratesgigas,wasidentifiedthroughitsabilitytoinhibithumanclassECa2+channelsstablyexpressedinamammaliancellline.AnIC50of15-30nMwasobtainedforblockoftheclassECa2+channel,usingeitherpatchclampelectrophysiologyorK+-evokedCa2+flux.Atlownanomolarconcentrations,SNX-482alsoblockedanativeresistantorR-typeCa2+currentinratneurohypophysealnerveterminals,butconcentrationsof200-500nMhadnoeffectonR-typeCa2+currentsinseveraltypesofratcentralneurons.ThepeptidehasthesequenceGVDKAGCRYMFGGCSVNDDCCPRLGCHSLFSYCAWDLTFSD-OHandishomologoustothespiderpeptidesgrammatoxinS1Aandhanatoxin,bothpeptideswithverydifferentionchannelblockingselectivities.NoeffectofSNX-482wasobservedonthefollowingionchannelactivities:Na+orK+currentsinseveralculturedcelltypes(upto500nM);K+currentthroughclonedpotassiumchannelsKv1.1andKv1.4expressedinXenopusoocytes(upto140nM);Ca2+fluxthroughL-andT-typeCa2+channelsinananteriorpituitarycellline(GH3,upto500nM);andBa2+currentthroughclassACa2+channelsexpressedinXenopusoocytes(upto280nM).AweakeffectwasnotedonCa2+currentthroughclonedandstablyexpressedclassBCa2+channels(IC50>500nM).TheuniqueselectivityofSNX-482suggestsitsusefulnessinstudyingthediversity,function,andpharmacologyofclassEand/orR-typeCa2+channels.
Newcomb,R., etal. (1998)SelectivepeptideantagonistoftheclassEcalciumchannelfromthevenomofthetarantulaHysterocratesgigas, Biochemistry. PMID:9799496
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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!
由弱酸及其盐、弱碱及其盐组成的混合溶液,能在一定程度上抵消、减轻外加强酸或强碱对溶液酸碱度的影响,从而保持溶液的pH值相对稳定。这种溶液称为缓冲溶液。
是否可以理解为纯化水得PH范围为6.3-7.6?能否直接用pH计测量?谢谢!
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?
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