The α-glucosidases of Dictyostelium discoideum: II. Developmental regulation and cellular localization☆

[摘要] Fourisozymesofα-glucosidaseinDictyosteliumdiscoideumhavebeenidentifiedandsomeoftheirenzymaticandphysicalpropertiescharacterized(R.H.BortsandR.L.Dimond,1981,Develop.Biol.87,176–184).Inthisreportthecellularlocalizationanddevelopmentalregulationofthreeoftheseisozymesaredetermined.α-Glucosidase-1isthemajorisozymeofvegetativeamoebae.Itislysosomallylocalizedandsecretedfromthecellundercertainconditions.IthasanacidicpHoptimumandcarriesthecommonantigenicdeterminantfoundonalllysosomalenzymesinthisorganism.Thespecificactivityofthisisozymebeginstodecreasewithinafewhoursaftertheinitiationofdevelopmentandisnolongerdetectableinthematurefruitingbody.α-Glucosidase-2hasaneutralpHoptimumandisneitherlysosomalnorsecreted.Ratheritismembraneboundandispossiblylocatedonthecisternalsideofmicrosomalvesicles.Thisisozymedoesnotpossessthecommonantigenicdeterminant.α-Glucosidase-2comprises20–40%ofthetotalα-glucosidaseactivityofthevegetativecell.Itsspecificactivityincreasesthreefoldduringdevelopment.Thisisozymeappearstobedevelopmentallycontrolledsinceitfailstoaccumulateinaggregationdeficientmutants.Itsaccumulationisalsodependentuponcontinuedproteinsynthesis.α-Glucosidase-4,likeα-glucosidase-1,hasanacidicpHoptimum.Itdoesnotappeartobelysosomallylocalizednormembranebound.Approximately30%oftheactivityisprecipitablebyantibodyagainstthecommonantigenicdeterminantindicatingthatitislesshighlymodifiedorfewermoleculesaremodified.Theisozymeisundetectableduringvegetativegrowthanddoesnotbegintoaccumulateuntillateaggregation.Activitypeaksinmaturefruitingbodieswhereitisthepredominantacidicα-glucosidaseactivity.Accumulationofα-glucosidase-4isblockedinmorphologicallydeficientmutantsandbyinhibitorsofproteinsynthesis.

[学科分类] 生物科学（综合）