Streptavidinisaproteinthathassimilarbindingpropertiestoeggwhiteavidin.Itisisolatedfromstreptomycesavidinii.Streptavidinhasamolecularweightof60kDaandhas4subunits.Eachsubunitcanbindonemoleculeofbiotin.Biotinisawater-solublevitamin.Streptavidinhasanextremelyhighbindingaffinity(Kd=10-15)forbiotin.Ithasprovenusefulinthedetectionofantigenscoupledwithbiotinylatedsecondaryantibodies.Thereareseveraladvantageswhenusingstreptavidinversusanavidincomplex(ABC).Incontrasttoavidin,streptavidinisnotglycosylatedandisthereforeunchargedatneutralpH(6.5versus10).Thislowersnonspecificbackgroundstaining.Streptavidinalsolackscarbohydratesidechainsthatmaybeanothercauseofnon-specificbackground.Anotherkeyadvantageofstreptavidinisthesignificantincreaseinsensitivity(probablyduetolesssterichindrance),thusfacilitatinganincreaseinoverallbindingcapacity.Finally,streptavidin-enzymeconjugatesaremuchmorestablethananABCcomplex.TheABCcomplexmustbefreshlymade30minutespriortouseandisstableonlyforafewdays.Incontrast,astreptavidin-conjugatecanbestoredforupto1-2years.Thereagentcomesinaready-to-useformat,thussavingtimeandpotentialmistakes.Biocare’sStarrTrekdetectionsystemhasbeendevelopedtoprovideasignificantincreaseinstainingsensitivity.StarrTrekUniversalDetectionsystemcanbeusedwithbothmouseandrabbitprimaryantibodies.Afterlabelingtheantigenwithaprimaryantibody,auniversal,affinity-purified,biotinylatedsecondaryantibodyisaddedtobindtotheprimaryantibody.HorserADIshperoxidase(HRP)labeled-streptavidinisthenaddedtobindtothebiotinylatedsecondaryantibody.Achromogen/substrateisthenappliedandreactswithaspecificenzymetoproduceanintensecolorsignal.StarrTrekdetectionsystemsworkwellwithparaffin-embeddedtissues,frozensectionsandcellpreparations.StarrTrekuniversaldetectionsystemscanbeusedwithBioGenexandDakopredilutedorconcentratedantibodiesatasignificantcostreduction.