| 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.
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