chapter3.enzyme

1、2024/3/5,1,Chapter 3. enzyme,CompositionCharacteristics and mechanism Kinetics of enzyme-catalzed reactionRegulationNames and classesEnzyme and medicine,2024/3/5,2,introduction,biocatalyst生物催化劑: enzyme and ribozyme

2、核酶Enzyme---proteins having catalytic activityRibozyme---nucleic acids having catalytic activity,2024/3/5,3,1926, Sumner美國,脲酶結(jié)晶，酶是蛋白質(zhì),1930年Northrop等得到了胃蛋白酶、胰蛋白酶和胰凝乳蛋白酶的結(jié)晶，進一步證明了酶是蛋白質(zhì),J.B.Sumner,J.H.Northrop,Enzyme is pr

3、otein.,2024/3/5,4,Thomas Cech University of Colorado at Boulder, USA,Sidney Altman Yale University New Haven, CT, USA,1982年T.Cech等人發(fā)現(xiàn)四膜蟲的rRNA前體能在完全沒有蛋白質(zhì)的情況下進行自我加工，發(fā)現(xiàn)RNA有催化活性1983年S.Altman等研究RNaseP（20%蛋白質(zhì)和80%RNA），發(fā)現(xiàn)

4、RNaseP中的RNA可催化E. coli tRNA的前體加工,ribozyme,2024/3/5,5,Section 1 molecular structure and function,Monomeric enzyme單體酶：one peptide chainOligomeric enzyme寡聚酶：many subunitsMultienzyme system多酶體系：complex of enzymes of differ

5、ent function.Multifunctional enzyme多功能酶 / Tandem enzyme串聯(lián)酶: function different enzymes in one peptide chain.,2024/3/5,6,Ⅰ. Molecular composition of enzymes,enzyme,Simple enzyme單純酶,Conjugated enzyme結(jié)合酶,apoenzyme酶蛋白,cofa

6、ctor輔助因子,,,metal ion金屬離子,,Small organic molecules　有機小分子,Holoenzyme全酶active,inactive,2024/3/5,7,Metalloenzyme金屬酶:　bind metal ion tightlyMetal activated enzyme金屬激活酶: don’t bind metal ion tightly, but the metal ion is es

7、sential to the enzyme activity.,Functions of metal ion:As active center, join in electron transfer,group tansfer and so on.Stablize steric structure of apoenzyme.Help the substrate binding.Neutralize anion, to lower

8、static electricity repulsion of the reaction.,2024/3/5,8,2024/3/5,9,Prosthetic group輔基,coenzyme輔酶,cofactor,,2024/3/5,10,Ⅱ. Active center of enzymes,2024/3/5,11,Section 2. characteristics and mechanism of enzyme-catalyze

9、d reaction,酶與一般催化劑的共同點common characters of enzymes and general catalysts：反應前后沒有質(zhì)和量的變化the quality and mass of catalysts before the reaction are identical to that after reaction. 只能催化熱力學允許的反應catalyze the reaction thermo

10、dynamics-permissive only.只能加速可逆反應的進程，而不能改變反應的平衡點Accelerate reversible reaction proceeding, but can’t change the point of balance.,2024/3/5,12,Ⅰ. Characteristics of enzyme-catalyzed reaction,High efficiency,比非催化反應高108～10

11、20倍； 可比一般催化劑高106～1013倍,尿素水解脲酶／Ｈ＋：７?１０１２,苯酰胺水解α-胰凝乳蛋白酶／Ｈ＋：6?106,25℃時，活化能每減少4.18kJ/mol,反應速度增加5.4倍．,2024/3/5,13,Specificity專一性,Absolute specificity: 一種底物Relative specificity：一類底物Stereospecificity：對立體異構(gòu)體有選擇性,The e

12、nzyme-catalyzed reaction can be regulated可調(diào)節(jié)性,2024/3/5,14,Ⅱ. Mechanism of enzyme-catalyzed reaction,Induced-fit hypothesis for forming of enzyme-substrate complex,酶在與底物相互接近時，其結(jié)構(gòu)相互誘導、相互變形和相互適應，進而相互結(jié)合。,2024/3/5,15,Reactio

13、n mechanism,鄰近效應proximity effect與定向排列orientation arrange,多元催化multielement catalysis與協(xié)同作用cooperation,表面效應surface effect,2024/3/5,16,Section 3. kinetics of enzyme-catalyzed reactions,Ⅰ. Influence of substrate concentration

14、 on reaction velocity,當?shù)孜餄舛群苄r，為一級反應．V= k [S]隨底物濃度逐漸增大，變?yōu)榛旌霞壏磻數(shù)孜餄舛群艽髸r，為零級反應.v= k.,2024/3/5,17,1. Michaelis equation米－曼氏方程式,1913, L. Michaelis and M.L.Menten,2024/3/5,18,2024/3/5,19,2024/3/5,20,2024/3/5,21,2. Meaning

15、of Km and Vm,Km equal to [S] when the velocity is half of the Vmax. (mol/L),Km的大小反映該酶對底物親和力的大小the value of Km weigh the affinity of enzyme with substrate.,If K2 >> K3,,Km值是酶的特性常數(shù)，只與酶的結(jié)構(gòu)、底物和反應環(huán)境有關(guān)，與酶的濃度無關(guān)。在10-6~10-2

16、mmol/L之間。,2024/3/5,22,Vm, Vmax, 最大反應速度，酶完全被底物飽和時的反應速度．,K3, 轉(zhuǎn)換數(shù) turnover number:　　當酶被底物充分飽和時，單位時間內(nèi)每個酶分子催化底物轉(zhuǎn)變?yōu)楫a(chǎn)物的分子數(shù)．大多數(shù)在1~104/s之間．,2024/3/5,23,3. Determination of Km and Vm,,,,,,2024/3/5,24,Ⅱ. influence of enzyme conce

17、ntration,v = k3 [E], as [S]>>[E],2024/3/5,25,Ⅲ. Influence of temperature,Optimum temperature最適溫度，most of them are in the range from 35 to 45℃ .,2024/3/5,26,Ⅳ. Influence of pH,Optimum pH最適pH常為中性，胃蛋白酶為1.8, 肝精氨酸酶為9.8

18、．,2024/3/5,27,Ⅴ. Influence of inhibitors,Inhibitor抑制劑： the matters which decrease enzyme activity, but don’t make the enzyme denatured.,Irreversible inhibition,Reversible inhibition可逆性抑制 competitive inhibition競爭性

19、抑制 non-competitive inhibition非競爭性抑制 uncompetitive inhibition反競爭性抑制,,2024/3/5,28,1. Irreversible inhibition,Irreversible inhibition: the inhibitor combine with essential group of enzyme active center by covalen

20、t bond, resulting in enzymatic activity loss.,2024/3/5,29,2. Reversible inhibition,Reversible inhibition: the inhibitor combine with enzyme,or enzyme-substrate complex by non-covalent bond, resulting in enzymatic act

21、ivity decrease or loss. the inhibitor can be removed by dialysis, or ultrafiltration,competitive inhibition競爭性抑制 non-competitive inhibition非競爭性抑制 uncompetitive inhibition反競爭性抑制,2024/3/5,30,(1) competitive inhibitio

22、n,competitive inhibition: the structure of inhibitor is similar to substrate. This make it combine with enzyme competively to substrate.,2024/3/5,31,Characteristics of competitive inhibition,Inhibitor structure is

23、similar to that of substrateDegree of inhibition is determined by their affinity and substrate concentration. Vmax is invariable, apparent Km increase.,2024/3/5,32,2024/3/5,33,2024/3/5,34,(2)non-competitive inhibition

24、非競爭性抑制,2024/3/5,35,Characteristics of non-competitive inhibition,Inhibitor combine with essential groups out of active center, no competitive .Degree of inhibition is determined by the concentration of inhibitor.Vmax d

25、ecrease, Km is invariable,2024/3/5,36,(3)uncompetitive inhibition反競爭性抑制,2024/3/5,37,Characteristics of uncompetitive inhibition,Inhibitor combine with enzyme-substrate complex only.Degree of inhibition is determined by

26、concentration of both inhibitor and substrate.Vm decrease, Km decrease.,2024/3/5,38,2024/3/5,39,Ⅵ. Influence of activator,Activator激活劑：substance which change enzymes inactive into active state, or which increase enzyme

27、activity, such as Mg2+, K+, Cl-.,Essential activator Non-essential activator,2024/3/5,40,Ⅶ. Determination of enzyme activity ; enzyme activity unit,The enzyme activity is determined by the reaction ratio.,1國際單位 IU = 在特定

28、條件下，每分鐘催化1μmol底物轉(zhuǎn)化為產(chǎn)物所需要的酶量．Quantity of enzyme which can catalyze 1μmol substrate change into product at certain condition.,1催量kat＝在特定條件下，每秒鐘催化1mol底物轉(zhuǎn)化為產(chǎn)物所需要的酶量．,1IU = 16.67 ? 10-9 kat,2024/3/5,41,Section 4. the regula

29、tion of enzyme,Regulated target: key enzyme,Ways of regulation:,Regulation of enzyme activity (fast).,Regulation of enzyme quantity (slow).,,2024/3/5,42,Ⅰ. Regulation of enzyme activity,1.Zymogen and activation of zymoge

30、n酶原與酶原激活,Zymogen: 有些酶在細胞內(nèi)合成或剛分泌時，無催化活性，這種無催化活性的酶的前體．,activation of zymogen： the process of inactive zymogen change into active enzyme, also the process of forming or exposing active center.,2024/3/5,43,2024/3/5,44,2. A

31、llosteric regulation變構(gòu)調(diào)節(jié),效應劑,,變構(gòu)酶,調(diào)節(jié)亞基,催化亞基,2024/3/5,45,2024/3/5,46,3. Regulated by covalent modification of enzyme,磷酸化phosphorylation ? 脫磷酸化dephosphorylation乙?；痑cetylation ? 脫乙酰化產(chǎn)deacetylation甲基化methylation ? 脫甲基化deme

32、thylation腺苷化adenosination ? 脫腺苷化deadenosinationRSH ? RS-SR,2024/3/5,47,2024/3/5,48,Ⅱ. Regulation of enzyme quantity,Induce or repress synthesis of apoenzyme,Regulation of enzyme degradation,2024/3/5,49,Ⅲ. Isoenzyme同工酶,

33、Isoenzyme: enzymes which catalyze same reaction, but their molecule structure, physico-chemical property　and immunology charcter are different.they must be the enzymes encoded by different genes or mRNA, exist in differ

34、ent tissues of a body,or in different subunits of a cell.,2024/3/5,50,Section 5. naming and classification of enzyme,Ⅰ. 命名習慣名稱?推薦名稱系統(tǒng)命名法：底物：底物　反應性質(zhì)．,2024/3/5,51,2024/3/5,52,Ⅱ. classification,氧化還原酶oxidoreductases轉(zhuǎn)移酶t

35、ransferases水解酶hydrolases裂解酶lyases：催化從底物移去一個基團并留下雙鍵的的反應或其逆反應．異構(gòu)酶isomerases合成酶ligases,2024/3/5,53,Section 6. relation of enzyme with medicine,Ⅰ. Enzyme and disease,Enzyme and diseases occurrence Enzyme and diseases di

36、agnosis Enzyme and diseases treatment,2024/3/5,54,Ⅱ. Application of enzyme in medicine,used in clinical test as reagentUsed in clinical treatment as medicineUsed in scientific research and production 工具酶　酶標記測定法　

37、固定化酶　抗體酶,2024/3/5,55,選擇題練習酶化學,2024/3/5,56,,A．所有蛋白質(zhì)都有酶的活性 B．其底物都是有機化合物C．其催化活性都需要特異的輔助因子D．體內(nèi)所有具有催化活性的物質(zhì)都是酶E．酶是由活細胞合成具有催化作用的蛋白質(zhì),1. 關(guān)于酶概念的敘述下列哪項是正確的？,2024/3/5,57,,A．所有酶的活性中心都有金屬離子 B．所有的抑制劑都作用于酶的活性中心C．所有的必需集團都位于酶的活性

38、中心 D．所有酶的活性中心都含有輔酶E．所有的酶都有活性中心,2．關(guān)于酶活性中心的敘述下列哪項是正確的？,2024/3/5,58,,3. 酶加速化學反應的根本原因是( ),A. 升高反應溫度 B. 增加反應物碰撞頻率 C. 降低催化反應的活化能D. 增加底物濃度 E. 降低產(chǎn)物的自由能,2024/3/5,59,,4. Holoenzyme refer to ( ),A. Complex of

39、 enzyme with substrateB. Complex of enzyme with suppressant C. Complex of enzyme with cofactorD. Inactive precursor of enzyme Complex of enzyme with allosteric effector,2024/3/5,60,,5. 金屬離子作為輔助因子的作用錯誤的是( ),A.

40、 作為酶活性中心的催化基團參加反應 B. 與穩(wěn)定酶的分子構(gòu)象無關(guān)C. 可提高酶的催化活性D. 降低反應中的靜電排斥E. 可與酶、底物形成復合物,2024/3/5,61,,6. 活化能的概念是指( ),A. 底物和產(chǎn)物之間能量的差值 B. 參與反應的分子所需的總能量C. 分子由一般狀態(tài)變成活化態(tài)所需能量 D. 溫度升高時產(chǎn)生的能量E. 以上都不是,2024/3/5,62,,7. 酶促

41、反應動力學所研究的是( ),A. 酶的基因來源 B. 酶的電泳行為 C. 酶的誘導契合D. 酶分子的空間結(jié)構(gòu) E. 影響酶促反應速度的因素,2024/3/5,63,,8. Michaelis-Menten enzyme kinetics diagram of curves is a ( ),A. straight line B. rectangular hyperbola

42、 C. S shape curve D. parabola E. Not above all,2024/3/5,64,,9. 關(guān)于Km的意義正確的是( ),A. Km為酶的比活性 B. 1/Km越小,酶與底物親和力越大C. Km的單位是mmol/min D. Km值是酶的特征性常數(shù)之一E. Km值與酶的濃度有關(guān),2024/3/5,65,,10. 競爭性抑制劑的特點是( ),A.

43、 抑制劑以共價鍵與酶結(jié)合 B. 抑制劑的結(jié)構(gòu)與底物不相似C. 當抑制劑的濃度增加時,酶變性失活 D. 當?shù)孜餄舛仍黾訒r,抑制作用不減弱E. 抑制劑和酶活性中心外的部位結(jié)合,2024/3/5,66,,11. In anticompetitive inhibition of enzyme, the reaction kinetics parameter change as ( ),Km↑,Vmax in

44、variably Km↓,Vmax↓ Km invariably,Vmax↓D. Km↓,Vmax invariably E. Km↓,Vmax↑,2024/3/5,67,,12. 有機磷農(nóng)藥與酶活性中心結(jié)合的基團是( ),A. 組氨酸上的咪唑基 B. 賴氨酸上的ε-氨基 C. 絲氨酸上的羥基D. 半胱氨酸上的巰基 E. 谷氨酸上的γ-羧基,2024/3/5,68,,13.

45、 關(guān)于變構(gòu)酶的論述錯誤的是( ),A. 變構(gòu)酶為多亞基組成B. 如底物與一亞基結(jié)合后,使其他亞基迅速與底物結(jié)合程正協(xié)同效應C. 正協(xié)同效應的底物濃度曲線呈矩形雙曲線D. 底物與一亞基結(jié)合后,使其亞基結(jié)合底物能力減少稱負協(xié)同效應E. 變構(gòu)效應劑與一亞基結(jié)合后,使酶其他亞基迅速與底物結(jié)合為異促協(xié)同效應,2024/3/5,69,,14. –SH is one enzyme’s essential group.

46、Which substance can protect this enzyme from oxidation?,A. Cys B. GSH C. urea D. ionic detergentE. ethanol,2024/3/5,70,,15. 快速調(diào)節(jié)可通過( ),A. 磷酸化與去磷酸化 B. 腺苷酸化與腺苷酸化 C. 變構(gòu)調(diào)節(jié)D. 改變酶的合成速度 E. 酶促反應的可調(diào)節(jié)性,

47、2024/3/5,71,,16. The characteristic constants of enzymes include ( ),A. Enzymic optimum temperatureB. Enzymic optimum pH C. Vmax D. Km E. KS,2024/3/5,72,,,17. 磺胺藥的抑菌機理是( ),A. 競爭性抑制二氫葉酸合成酶的活性B. 干擾體內(nèi)核酸

48、的代謝C. 結(jié)構(gòu)與二氫葉酸相似D. 抑制程度強弱取決于藥物與酶底物濃度的相對比例E. 磺胺藥是二氫葉酸合成酶的變構(gòu)抑制劑,2024/3/5,73,,18. Cofactors of enzyme are ( ),A. Micromolecule organic compounds B. metal ionC. vitamine D. various kinds of organic and inorgani

49、c compounds E. A kind of conjugated protein,2024/3/5,74,,19. 某種酶的活性依賴于酶活性中心的必需基團-SH,能保護此酶不被氧化的物質(zhì)是( ),A. GSH B. 維生素C C. 半胱氨酸 D. 維生素A E. 兩價陽離子,2024/3/5,75,,,20. 酶分子上必需基團的作用是( ),A. 與底物結(jié)合 B. 催化底物