氨基酸代谢Metabolism-of-Amino-Acids

氨基酸代谢MetabolismofAminoAcids,Chapterseven,Topics,NutritionalFunctionofProteinDigestion,AbsorptionandPutrefactionofProteinsGeneralMetabolismofAminoAcidsMetabolismofAmmoniaMetabolismofIndividualAminoAcids,蛋白质的营养作用NutritionalFunctionofProtein,Partone,蛋白质营养的重要性,1.维持细胞、组织的生长、更新和修补,2.参与多种重要的生理活动,催化（酶）、免疫（抗原及抗体）、运动（肌肉）、物质转运（载体）、凝血（凝血系统）等。,3.氧化供能人体每日18%能量由蛋白质提供。,氮平衡(nitrogenbalance)Tomeasurenitrogenbalance,measuretheamountofNgoingin(justmeasureamountofproteinconsumed)andNgoingout(ureaintheurine).,Innormaladults,nitrogenintakematchesnitrogenexcreted.,氮正平衡Positivenitrogenbalanceingestednitrogenexcretednitrogen（growthandpregnancy）,氮负平衡Negativenitrogenbalanceingestednitrogenacetoacetate),苯酮酸尿症(phenylkeronuria,PKU),causedbyadefectinthehydroxylationofphenylalaninetomaketyrosine苯丙氨酸羟化酶缺陷.Whenphenylalaninecannotbeconvertedtotyrosine,itundergoestransamination,andtheresultingketo-acidproducesphenylketoneswhichappearintheurine.Thediseaseproducesmentalretardationamongothersymptoms.,2.Tryptophanmetabolism,色氨酸,5-羟色胺,一碳单位onecarbonunit,丙酮酸+乙酰乙酰CoA,维生素PPniacin,glucogenic(-Ala-pyruvate)ketogenic(-acetoacetyl-CoA)vitaminogenic!(-niacin),Tryptophan,5-hydroxytryptamine,支链氨基酸,V.Branchedchainaminoacidsmetabolism,step1:transaminase-keto-acidstep2:oxidativedecarboxylation,Themusclehasaveryactivebranchedchainaminoacidmetabolicpathwayandusesthatpathwaytoprovideenergyforitsownuse.,Maplesyrupurine槭糖尿,Maplesyrupurinediseaseresultsfromalackoftheketo-aciddehydrogenaseandaninabilitytometabolizebranchedchainaminoacids.Theketo-acidswhichaccumulateareexcretedintheurine.Theyhavecharacteristicodors,whichrangefrommapletocheesy.Thediseasecanresultinpoormyelination髓鞘形成andmentalretardation.,氨基酸的重要含氮衍生物,+NO,+O2,NADPH+H+NADP+,一氧化氮合酶（NOS）,精氨酸,瓜氨酸,一氧化氮,Allof20kindsofaminoacidsaredegradedbydifferentpathwaysthatconvergetojust7metabolicintermediates:Pyruvate,Acetyl-CoA,Acetoacetate,-ketoglutarate,Succinyl-CoA,Fumarate,andOxaloacetate,Howdoesaminoacidcatabolismleadintopathwaysofenergypro