生物化學(xué)教學(xué)課件：復(fù)習(xí)課

1、Protein breakdown starts at stomachOptimal pH1.52.5，Low specificityProduce small peptide and free amino acids pepsinogen胃蛋白酶原+ Small PeptideHCl、PepsinPepsinBreakdown of dietary proteins Enterokinase腸激酶 : produced by cells of the duodenum du:di:nm （十二指腸）Synthesis of the enzymes as inactive precursors

2、-zymogen(酶原或前酶）:1 Protects the exocrine cells from destructive proteolytic attack. 2 Transportation3 Allow RegulationElaborate mechanism for getting active digestive enzymes.Protein Digestion Proteolytic enzymes of pancreatic juiceEndopeptidasesExopeptidasesTrypsin : Arg, Lys (C)Chymotrypsin : Tyr,

3、Trp, Phe, Met, Leu (C)Elastase: Ala, Gly, Ser (C)carboxypeptidaseaminopeptidaseCleavage sites and substrates of proteasesMARTKQTARKSTGGKAPRKQLATKAARKSAPSTGTwo major systems for the turnover of cellular proteins:Lysosomes and Ubiquitin-mediated protein degradationProtein Degradation in Cell1 Lysosoma

4、l hydrolasesexhibit acidic pH optimal.2 Lost activity if leaked into cytosol.3 Cathepsin 組織蛋白酶家族Low specificityLysosomal Degradation PathwayProteinsA. EndocytosedB. Cytosolic C. Organelles by autophagy溶酶體貯積病：基因突變致溶酶體酸性水解酶缺陷痛風(fēng)：溶酶體破裂Ubiquitination Ub activating enzyme(Uba) Ub conjugating enzyme(Ubc) E

5、3- Ub LigaseWhat is Ubiquitin and Ubiquitylation?Human Ub: MQIFKVTLTGKTITLEVEPNDTIENVKAKIQDKEGIPPDQQRLIFAGKQLEDGRTLADYNIQKESTLHLVLRLRGGYeast Ub: MQIFKVTLTGKTITLEVESSDTIDNVKSKIQDKEGIPPDQQRLIFAGKQLEDGRTLSDYNIQKESTLHLVLRLRGG肽鍵和異肽鍵substrateUbMQIFKVTLTGKTITLEVEPNDTIENVKAKIQDKEGIPPDQQRLIFAGKQLEDGRTLADYNIQ

6、KESTLHLVLRLRGGUbiquitin pathwayE1-S-UbE2-S-UbE3substratesUbMono-ubiquitinationChange：protein conformation,Localization, interactionPolyubiquitinationUbUbUbUbsubstratesProteosomeDegradationE1- Ub activating enzyme(Uba)Uses ATPAMP+PPi to form thioester bond between its sulfhydryl group and the termina

7、l carboxylate group of UBE2- Ub conjugating enzyme(Ubc):Accepts activated UBE3- Ub Ligase: Catalyzes transfer of UB from E2 to -amino group of lysine on target protein forming an isopeptide bond異肽鍵ATP蛋白質(zhì)泛素化降解途徑7要素Amino acid metabolism Deamination（脫氨） Transamination（轉(zhuǎn)氨作用） Urea cycle（尿素循環(huán)） Pyruvate gr

8、oup a Ketoglutarate group Succinyl-CoA group Oxaloacetate group Fumarate / oxaloacetate group Alanine / acetoacetate group Acetyl-CoA / acetoacetate group DecarboxylationTransamination(轉(zhuǎn)氨作用）ALT: Alanine aminotransferase (in liver) 丙氨酸氨基轉(zhuǎn)移酶，also called glutamate-pyruvate transaminase（谷丙轉(zhuǎn)氨酶）, GPTAST:

9、Aspartate aminotransferase (in heart) ，also called glutamate-oxaloacetate transaminase（谷草轉(zhuǎn)氨酶）, GOTTwo important transaminases:Transamination-needs coenzyme pyridoxal phosphate（磷酸吡哆醛， B6）1 Covalent ligated to enzyme2 Interaction with enzyme3 Schiffs baseVitamine B6亞胺(2) Oxidative deaminationGlutamate

10、 Releases Its Amino Group as Ammonia in the Liver1 In hepatocytes mitochondria, 2 Glutamate undergoes oxidative deamination 3 Catalyzed by L-glutamate dehydrogenase4 Produces free ammonia5 Need NAD and Produces NADH 6 Required for Urea Cycle7 The enzyme is strictly regulated by energy (ADP, ATP)Meta

11、bolism of Ammoniamost vertebratesbirds & reptilesfish & other aquatic vertebrates1 Glucose-Alanine CycleAlanine Transports Ammonia fromSkeletal Muscles to the Liver1 Glucose Alanine cycle2 Transportation of ammonia by Gln 丙氨酸：NeutralNon-polarityNon-toxicEasily transported through membrane2. Transpor

12、tation of ammonia by GlnExcess ammonia in tissues is added to glutamate to form glutamine, catalyzed by glutamine synthetase(谷氨酰胺合成酶） After transport in the bloodstream,the glutamine enters the liver and NH4 is liberated in mitochondria by the enzyme glutaminase（谷氨氨酰胺酶）Formation of urea1. Site: live

13、r (mitochondria and cytosol)2. Process - ornithine cycleUrea Is Produced from Ammonia in Five Enzymatic Steps(氨、瓜、精琥、精、尿）Hans Creb1 The 2 N of urea : NH3 and Asp.2 Starts/ends up with: ornithine3 NH3, CO2 form caramoyl phosphate,4 Citrulline formation,5 Incorporation of Asp.6 Energy consuming: One u

14、rea 3ATP, 4 P7 Needs 5 enzymes：carbamoyl phosphate synthetase ornithine carbamoyl transferase, OCTArgininosuccinate SynthetaseArgininosuccinaseArginase8 Rate limiting :1st step9 mitochondrianl vs cytosolUrea formation:Regulation of urea synthesisActivation of the urea cycle by N-acetyl-glutamateN-ac

15、etyl-glutamate synthetase IRegulation of urea synthesisEnergy consuming: one urea will costs 4 PCarbamoylphasphate synthetase ISubstrate activation/inductionResponsive to concentration of ammonia /amino acid in liverProtein-rich dietary Starvation Five final products of the backbone of amino acids:

16、connected to TCAAcetyl-CoAa-ketoglutarateSuccinyl-CoAFumarateOxaloacetateTetrahydrofolic acid (FH4) and one carbon unitOne carbon units are produced in catablite of AA and carried by FH4. One carbon units are substance for synthesis of nucleic acid.In great need of new-born蝶啶對(duì)氨基苯甲酸GlutamatePurine ri

17、ng甲基受體接受甲基甲硫氨酸腺苷甲硫氨酸AdoMet, SAMMethylatedacceptor高半胱氨酸FH4 provides methyl group for methionine, which servers as major methyl-group donor for many reactions, Branched Chain amino acid(支鏈氨基酸, BCAA)的起始途徑是相同的： aminotransferases 同工酶Branched keto acidsDehydrogenase支鏈氨基酸分解代謝酶缺乏并不多見，一旦發(fā)生可造成酸中毒；支鏈酮酸脫氫酶復(fù)合體活性

18、缺失導(dǎo)致楓樹蜜汁尿病：尿液具有特殊的楓樹蜜汁氣味，伴隨酸中毒，智力遲緩和短壽。限制膳食治療！PhenylKetonuria苯丙酮尿癥Phenylalanine HydroxylaseTyrosine AminotransferaseParahydroxyphenyle pyruvate Di-oxygenase (ascorbate Vc)Homogentisate DioxygenaseMaleyl Acetoacetate IsomaeraseFumaryl AcetoacetaseAlanineAsparagineAspartateCysteineGlutamateGlutamineGl

19、ycineProlineSerineTyrosineArginine*HistidineIsoleucineLeucineLysineMethioninePhenylalanineThreonineTryptophanValineEssential and Nonessential Amino Acids for Humans Essential Nonessential*Arg is essential in infants and growing children but not in adults. Most bacteria and plants can synthesize all

20、20 amino acids.AAs that an organism cannot synthesize under a given set of conditions are called “essential.” Those that can be synthesized in adequate amounts are “nonessential.”23 Humans can synthesize 10 of the 20 common amino acidsA, B, C 三種酶催化三步反應(yīng)；每種酶有2-3個(gè)同工酶；其中有一個(gè)酶是非變構(gòu)酶；當(dāng)Met高的時(shí)候，A2 and B1的合成被抑

21、制；當(dāng)Ile高的時(shí)候，C2的合成被抑制。End product inhibitionConcerted end product inhibitionGlutathione還原劑，可去除過(guò)氧化物維持紅細(xì)胞膜的穩(wěn)定性（抗過(guò)氧化物）酶的輔助因子，氨基酸跨膜運(yùn)輸，蛋白質(zhì)二硫鍵重排，GlutathioneTypes of Biological Nitrogen FixationFree-living (asymbiotic)CyanobacteriaAzotobacter固氮(細(xì))菌zutbktiSymbioticLegume-rhizobialegjum raizubiRank of Biologic

22、al Nitrogen FixationN2 fixing systemNitrogen Fixation (kg N/ha/year)Rhizobium-legume50 - 600Cyanobacteria- moss苔10 - 300Rhizosphere根系 associations5 - 25Free- living0.1 - 25Nodule MetabolismOxygen metabolismVariable diffusion barrierLegume-hemoglobinNitrogen metabolismNH3 diffuses to cytosolAssimilat

23、ionConversion to organic-N for transportCarbon metabolismFunctioning TCA in bacteroidsNitrogen FixationAll nitrogen fixing bacteria use highly conserved enzyme complex called NitrogenaseNitrogenase is composed of of two subunits: an iron-sulfur protein a molybdenum-iron-sulfur proteinSteps in Nitrog

24、en FixationNitrogenase:1 Nitrogenase: Two subunits, Exhangable of some subunit across species usually is not fully active as original2 Energy consume3 Amonia is the product4 Inactivated by O2 5 Inhibited by NH3 6 Amonia Assimilation-carried by Glutamate and GlutaminePurine DegredationAdenine deamina

25、seGuanine deaminaseXanthineOxidaseXanthineOxidaseUrateOxidaseXanthineAdenineGuanineUric acidAllantoinAllantoinase尿酸尿囊素Deamination OxidationFinal product:CytosineThymineUracilFinal：-amino acid, NH3, CO2PyrimidineDegradation二氫嘧啶脫氫酶二氫嘧啶酶脲基丙酸酶均缺乏選擇性-氨基異丁酸的唯一來(lái)源(評(píng)估抗腫瘤藥物殺細(xì)胞作用）CytosineUracil,ThymineDehydrog

26、enasehydrolaseTwo types of pathways lead to nucleotides:The de novo and the salvage pathways.De novo synthesis of nucleotides begins with the metabolic precursors: amino acids, ribose 5-phosphate, CO2, and NH3.Salvage pathways recycle the free bases and nucleosides released from nucleic acid breakdo

27、wn.次黃嘌呤核苷酸（5單磷酸肌苷）次黃嘌呤核苷酸腺苷琥珀酸合成酶IMP脫氫酶腺苷琥珀酸黃嘌呤核苷酸GMP formation requires enough ATP! AMP formation requires enough GTP!Salvage pathway of purins腺嘌呤磷酸核糖轉(zhuǎn)移酶APRT次黃嘌呤鳥嘌呤磷酸核糖轉(zhuǎn)移酶HGPRTRegulation of purine nucleotideBiosynthesis:coordination of deno vo and salvage pathwayBiogenesis of purinesAll the reactio

28、n occur in the cytosol of cellN10-Methyl-FH4 provides one carbon unitNeed amino acids: Gly, Gln, Asp, CO2The first nucleotide is IMP(肌苷單磷酸）:inosine-5-monophosphateCost a lot of energyMultiple functional enzymes 1st step PRPP to 5-phosphoribosylamine is limiting step: Gln-PRPP aminotransferasePRPP ac

29、tivates and IMP、AMP 、GMP inhibit the Gln-PRPP aminotransferase腺苷琥珀酸合成酶和IMP脫氫酶分別受到AMP和GMP的反饋抑制Defect in salvage pathway of purinsLesch(/leski/)-Nyhan syndrome自毀容貌綜合征:NO HGPRT Activity!1 produced by mutations in the HPRT gene located on the X chromosome2 Higher uric acid in boby3 Metal retardation4 Se

30、lf-mutilationThe GoutOverproduction of uric acidUric acid crystals precipitate into joints (Gouty Arthritis痛風(fēng)性關(guān)節(jié)炎), kidneys, ureters (stones結(jié)石)Adenine deaminaseGuanine deaminaseXanthineOxidaseAdenineSalvage pathway deficiency or Cancer treatment, Allopurinol :hypoxanthine analog Xanthine oxidase inhibitors binds to Xanthine Oxidase inhibit production of uric acid別嘌呤醇次黃嘌呤Pyrimidine biosynthesisCarbamoylphosphateAspartate1 由氨甲酰磷酸和天冬氨酸2 氨甲酰磷酸由氨甲酰磷酸合成酶II催化3 氨甲酰磷酸合成酶II存在于細(xì)胞質(zhì)中不同于氨甲酰磷酸合成酶I存在于線粒體中4 先合成嘧啶環(huán)UMP合成酶缺陷：遺傳性乳清