Overview | Apoptosisisanevolutionarilyconservedformofcellsuicide,whichfollowsaspecializedcellularprocess.Thecentralcomponentofthisprocessisacascadeofproteolyticenzymescalledcaspases.Theseenzymesparticipateinaseriesofreactionsthataretriggeredinresponsetopro-apoptoticsignalsandresultinthecleavageofproteinsubstrates,causingthedisassemblyofthecell(Sleeetal.1999).
CaspaseshavebeenidentifiedinorganismsrangingfromC.eleganstohumans.Themammaliancaspasesplaydistinctrolesinapoptosisandinflammation.Inapoptosis,caspasesareresponsIBLeforproteolyticcleavagesthatleadtocelldisassembly(effectorcaspases),andareinvolvedinupstreamregulatoryevents(initiatorcaspases).Anactivecaspaseconsistsoftwolargeandtwosmallsubunitsthatformtwoheterodimerswhichassociateinatetramer(Walkeretal.1994;Wilsonetal.1994;Rotondaetal.1996).Incommonwithotherproteases,caspasesaresynthesizedasprecursorsthatundergoproteolyticmaturation,eitherautocatalyticallyorinacascadebyenzymeswithsimilarspecificity(Kumar1999).
Caspaseenzymesspecificallyrecognizea4or5aminoacidsequenceonthetargetsubstratewhichnecessarilyincludesanasparticacidresidue.Thisresidueisthetargetforcleavage,whichoccursatthecarbonylendoftheasparticacidresidue(Thornberryetal.1997).Caspasescanbedetectedviaimmunoprecipitation,immunoblottingtechniquesusingcaspasespecificantibodies,orbyemployingFluorochromesubstrateswhichbecomefluorescentuponcleavagebythecaspase.
TestPrinciple:
CHEMICON"sInSituCaspaseDetectionKitsuseanovelapproachtodetectactivecaspases.ThemethodologyisbasedonFluorochromeInhibitorsofCaspases(FLICA).Theinhibitorsarecellpermeableandnon-cytotoxic.Onceinsidethecell,theinhibitorbindscovalentlytotheactivecaspase(Ekertetal.1999).Thiskitusesacarboxyfluorescein-labeledfluoromethylketonepeptideinhibitorofcaspase(FAM-VAD-FMK),whichproducesagreenfluorescence.Whenaddedtoapopulationofcells,theFAM-VAD-FMKprobeenterseachcellandcovalentlybindstoareactivecysteineresiduethatresidesonthelargesubunitoftheactivecaspaseheterodimer,therebyinhibitingfurtherenzymaticactivity.Theboundlabeledreagentisretainedwithinthecell,whileanyunboundreagentwilldiffuseoutofthecellandiswashedaway.Thegreenfluorescentsignalisadirectmeasureoftheamountofactivecaspasepresentinthecellatthetimethereagentwasadded.Cellsthatcontaintheboundlabeledreagentcanbeanalyzedby96-wellplate-basedfluorometry,fluorescencemicroscopy,orflowcytometry.
Application:
TheCHEMICONInSituFLICAPan-CaspaseDetectionKitisafluorescent-basedassayfordetectionofactivecaspasesincellsundergoingapoptosis.Thekitisforresearchuseonly.Notforuseindiagnosticortherapeuticprocedures. |