BackgroundInformation | Gutamicaciddecarboxylase(GAD;E.C.4.1.1.15)istheenzymeresponsIBLefortheconversionofglutamicacidtogamma-aminobutyricacid(GABA),themajorinhibitorytransmitterinhigherbrainregions,andputativeparacrinehormoneinpancreaticislets.TwomolecularformsofGAD(65kDaand67kDa,64%aaidentitybetweenforms)arehighlyconservedandbothformsareexpressedintheCNS,pancreaticisletcells,testis,oviductandovary.Theisoformsareregionallydistributedcytoplasmicallyinthebrainsofratsandmice(Sheikh,1999).GAD65isanamphiphilic,membrane-anchoredprotein(585a.a.),encodedonhumanchromosome10,andisresponsibleforvesicularGABAproduction.GAD67iscytoplasmic(594a.a.),encodedonchromosome2,andseemstoberesponsibleforsignificantcytoplasmicGABAproduction.GADexpressionchangesduringneuraldevelopmentinratspinalcord.GAD65isexpressedtransientlyincommissuralaxonsaroundE13butisdownregulatedthenextdaywhileGAD67expressionincreasesmostlyinthesomataofthoseneurons(Phelps,1999).Inmatureratpancreas,GAD65andGAD67appeartobedifferentiallylocalized,GAD65primarilyininsulin-containingbetacellsandGAD67inglucagon-containing(A)cells(Li,1995).GAD67expressionseemstobeparticularlyplasticandcanchangeinresponsetoexperimentalmanipulation(forexampleneuronalstimulationortransection)ordiseaseprogressionandemergentdisorderslikeschizophrenia(Volk,2000).ColocalizationofthetwoGADisoformsalsoshowschangesinGAD65/GAD67distributionscorrelatedwithcertaindiseasestatessuchasIDDMandSMS. |