Overview | Apoptosisisanevolutionarilyconservedformofcellsuicide,whichfollowsaspecializedcellularprocess.Thecentralcomponentofthisprocessisacascadeofproteolyticenzymescalledcaspases.Theseenzymesparticipateinaseriesofreactionsthataretriggeredinresponsetopro-apoptoticsignalsandresultinthecleavageofproteinsubstrates,causingthedisassemblyofthecell(Arends&Wyllie1991).
CaspaseshavebeenidentifiedinorganismsrangingfromC.eleganstohumans.Themammaliancaspasesplaydistinctrolesinapoptosisandinflammation.Inapoptosis,caspasesareresponsIBLeforproteolyticcleavagesthatleadtocelldisassembly(effectorcaspases),andareinvolvedinupstreamregulatoryevents(initiatorcaspases).Anactivecaspaseconsistsoftwolargeandtwosmallsubunitsthatformtwoheterodimerswhichassociateinatetramer(Sleeetal.1999;Salvesen&Dixit1997;Alnemrietal.1996).Incommonwithotherproteases,caspasesaresynthesizedasprecursorsthatundergoproteolyticmaturation,eitherautocatalyticallyorinacascadebyenzymeswithsimilarspecificity(Sleathetal.1990).
Caspaseenzymesspecificallyrecognizea4or5aminoacidsequenceonthetargetsubstratewhichnecessarilyincludesanasparticacidresidue.Thisresidueisthetargetforcleavage,whichoccursatthecarbonylendoftheasparticacidresidue(Thornberryetal.1992).Caspasescanbedetectedviaimmunoprecipitation,immunoblottingtechniquesusingcaspasespecificantibodies,orbyemployingFluorochromesubstrateswhichbecomefluorescentuponcleavagebythecaspase.
TestPrinciple:
CHEMICON"sInSituCaspaseDetectionKitsuseanovelapproachtodetectactivecaspases.ThemethodologyisbasedonFluorochromeInhibitorsofCaspases(FLICA).Theinhibitorsarecellpermeableandnon-cytotoxic.Onceinsidethecell,theinhibitorbindscovalentlytotheactivecaspase(Rotondaetal.1996).Thiskitusesasulforhodamine-labeledfluoromethylketonepeptideinhibitorofcaspase(SR-VAD-FMK),whichproducesaredfluorescence.Whenaddedtoapopulationofcells,theSR-VAD-FMKprobeenterseachcellandcovalentlybindstoareactivecysteineresiduethatresidesonthelargesubunitoftheactivecaspaseheterodimer,therebyinhibitingfurtherenzymaticactivity.Theboundlabeledreagentisretainedwithinthecell,whileanyunboundreagentwilldiffuseoutofthecellandiswashedaway.Thegreenfluorescentsignalisadirectmeasureoftheamountofactivecaspasepresentinthecellatthetimethereagentwasadded.Cellsthatcontaintheboundlabeledreagentcanbeanalyzedby96-wellplate-basedfluorometry,fluorescencemicroscopy,orflowcytometry.
Application:
TheCHEMICONInSituFLICAPan-CaspaseDetectionKitisafluorescent-basedassayfordetectionofactivecaspasesincellsundergoingapoptosis.Thekitisforresearchuseonly.Notforuseindiagnosticortherapeuticprocedures. |