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1、F1FoATPSynthaseCopyright©1999-2007byJoyceJ.Diwan.Allrightsreserved.MolecularBiochemistryIF1FoATPSynthaseofmitochondria,chloroplasts,bacteria:WhentheelectrochemicalH+gradientisfavorable,F1FocatalyzesATPsynthesiscoupledtospontaneousH+fluxtowardthesideofthemembranewhereF1protrudes(e.g.,towardthemito
2、chondrialmatrix).IfnoDpHorDYexiststodrivetheforwardreaction,Keqfavorsthereverse,ATPhydrolysis(ATPase).Insomebacteria,thereversereactionhasaphysiologicalrole,providingamechanismforATP-dependentcreationofaprotongradientthatdrivesotherreactions.InhibitorsofF1Fo,thatblockH+transportcoupledtoATPsynthe
3、sisorhydrolysis,include:oligomycin,anantibioticDCCD(dicyclohexylcarbodiimide),areagentthatreactswithcarboxylgroupsinhydrophobicenvironments,formingacovalentadduct.Rolesofmajorsubunitsweredeterminedinstudiesofsubmitochondrialparticles(SMP).Inmitochondriatreatedwithultrasound,innermembranebreaks&re
4、sealsasvesicles,withF1ontheoutersurface.SinceF1ofintactmitochondriafacesthematrix,theseSMParesaidtobeinsideout.ByEMwithnegativestain,ATPSynthaseappearedas"lollipops"ontheinnermitochondrialmembrane,facingthematrix.Higherresolutioncryo-EMlatershowedeachlollipoptohave2stalks.SeeMovie.AfterremovalofF
5、1,theSMPmembranecontainingFoisleakytoH+.AddingbackF1restoresnormallowpermeabilitytoH+.ThusitwasestablishedthatFoincludesa“H+channel."F1,thelollipophead,whenextractedfromSMP,catalyzesATPhydrolysis(spontaneousreactionintheabsenceofanenergyinput).ThusF1containsthecatalyticdomain(s).Eitheroligomycino
6、rDCCDblockstheH+leakinmembranesdepletedofF1.Thusoligomycin&DCCDinhibittheATPSynthasebyinteractingwithFo.ATPsynthasecomplexesofbacteria,mitochondria&chloroplastsareverysimilar,withonlyminordifferences.Mitochondriaarebelievedtohaveevolvedfromsymbioticaerobicbacteriaingestedbyananaerobichostcell.The
7、limitingmembraneofthebacteriumbecametheinnermitochondrialmembrane.MitochondriacontainasmallDNAchromosome,butgenesthatencodemostmitochondrialproteinsareinthenucleus,consistentwithtransferofsomeDNAduringevolution.Looking
