Designation:E1759–95(Reapproved2003)StandardTestMethodforIsoasparticAcidinProteins:MethodfortheDeterminationofAsparagineDeamidationProducts1ThisstandardisissuedunderthefixeddesignationE1759;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.INTRODUCTIONThestorageofproteinsinaqueoussolutionsoftenresultsintheformationofisoasparticacidlinkageswithinthepolypeptidechainasaresultofthedeamidationofaspargineresiduesandtherearrangementofasparticacidlinkages.ThistestmeasurestheamountofisoasparticacidresiduesinaproteinorpeptidesolutionbytheuseoftheenzymeproteinisoaspartylmethyltransferaseandradioactiveS-adenosyl-L-methionine.1.Scope1.1Thistestmethodcoversthedeterminationofisoasparticacidresiduesinaproteinorpeptidesample.Thistestmethodisapplicableforthedeterminationofisoasparticacidresiduesinasampleintherangeof2.5–50µmol/L.Higherconcentra-tionscanbedeterminedfollowingdilution.Thereportedlowerrangeisbasedonsingle-operatorprecision.1.2ThevaluesstatedinSIunitsaretoberegardedasthestandard.1.3Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.2.Terminology2.1DefinitionsofTermsSpecifictoThisStandard:2.1.1isoasparticacidresidue—indicatesanasparticacidresidueinwhichlinkageofthepolypeptidechaintakesplacethroughthegammacarboxylgroupoftheasparticacidversusthealphacarboxylgroupthatisusedinthenormalpeptidelinkage.3.SummaryofTestMethod3.1ThebasisoftheproceduregiveninthistestmethodistheproductionofradioactivemethanolequaltotheamountofisoasparticacidresiduespresentinaproteinsamplethroughtheactionoftheenzymeproteinisoaspartylmethyltransferaseandradiolabelledS-adenosyl-L-methionine,aradiolabelledformofa...
