编号：XY-0813R
Caseinisthenameforafamilyofrelatedphosphoproteins(αS1,αS2,β,κ).Theseproteinsarecommonlyfoundinmammalianmilk,makingup80%oftheproteinsincowmilkandbetween20%and45%oftheproteinsinhumanmilk.Caseinhasawidevarietyofuses,frombeingamajorcomponentofcheese,touseasafoodadditive,toabinderforsafetymatches.Asafoodsource,caseinsuppliesaminoacids;carbohydrates;andtwoinorganicelements,calciumandphosphorus.
Subunit:Caseincontainsafairlyhighnumberofprolineresidues,whichdonotinteract.Therearealsonodisulfidebridges.Asaresult,ithasrelativelylittletertiarystructure.Itisrelativelyhydrophobic,makingitpoorlysolubleinwater.Itisfoundinmilkasasuspensionofparticlescalled"caseinmicelles"whichshowonlylimitedresemblancewithsurfactant-typemicellaeinasensethatthehydrophilicpartsresideatthesurfaceandtheyarespherical.However,insharpcontrasttosurfactantmicelles,theinteriorofacaseinmicelleishighlyhydrated.Thecaseinsinthemicellesareheldtogetherbycalciumionsandhydrophobicinteractions.Severalmodelsaccountforthespecialconformationofcaseininthemicelles.Oneofthemproposesthemicellarnucleusisformedbyseveralsubmicelles,theperipheryconsistingofmicrovellositiesofκ-casein.Anothermodelsuggeststhenucleusisformedbycasein-interlinkedfibrils.Finally,themostrecentmodelproposesadoublelinkamongthecaseinsforgellingtotakeplace.Allthreemodelsconsidermicellesascolloidalparticlesformedbycaseinaggregateswrappedupinsolubleκ-caseinmolecules.
Theisoelectricpointofcaseinis4.6.Sincemilk'spHis6.6,caseinhasanegativechargeinmilk.Thepurifiedproteiniswaterinsoluble.Whileitisalsoinsolubleinneutralsaltsolutions,itisreadilydispersibleindilutealkalisandinsaltsolutionssuchassodiumoxalateandsodiumacetate.
Theenzymetrypsincanhydrolyzeoffaphosphate-containingpeptone.Itisusedtoformatypeoforganicadhesive.
酪蛋白(casein)是牛乳包括牛初乳的主要成分，通常在分离提取乳清过程中可得到大量的酪蛋白，它具有各种必需氨基酸，且组分合理，是一种优质的动物蛋白。然而，由于人体尤其是儿童对牛乳酪蛋白的分解能力较弱，牛乳酪蛋白的应用并不广泛。近来国外文献报道，牛乳酪蛋白短链肽除了易吸收外，还具有某些重要的生物学功能，提示着酪蛋白除单纯营养作用之外的广阔应用前景。
