CH6-Gangan生化课件-酶.ppt

1、酶 - Enzyme,Zhangguangxian Ph.D QQ: 99811075 Tel教学大纲目的要求,掌握酶化学本质、组成及酶促反应特点 熟悉酶促反应动力学 了解酶的催化机制、命名、分类以及与医学的关系,Structure of Enzyme,Robizyme,羧肽酶,Definition of Enzyme,酶：由活细胞具有催化活性的蛋白质 分类： 生物催化剂：蛋白质(酶)和核酸 酶分子组成：单纯酶和结合酶 化学本质：蛋白质 具有蛋白质所有的理化性质和生物学特征,Components of Enzyme,Holoenzyme Cojugated enzym

2、e,Simple enzyme,底 物,活性中心以外的必需基团,结合基团,催化基团,活性中心,Some terms should be noticed,Holoenzyme Apoenzyme and cofactor Cofactor：Ions; coenzyme/prosthetic group Active center binding group and catalytic group,Characteristics of enzymatic reaction,Instability (protein) High efficiency (G= H-T S) High specifici

3、ty Absolute: catalyze one specific substrate/reaction Relative: catalyze one kind of bond/compounds Stereo/optical: “three-point attachment” Regulable (multi-level and multi-mechanism; multiple options are available ),活化能：底物从初态转变到活化态所需的能量,High specificity,Active center: Binding group - bind Catalyti

4、c group - catalyse,Regulable - allosteric regulation,Mechanism of catalytic reaction,How do the E-S bind with each other: lock-key model induced-fit model Factors responsible for high efficiency Proximity and Orientation Transition-state stabilization,Some terms,Zymogen and activation Zymogen: An in

5、active precursor of an enzyme. particularly a proteolytic enzyme Activation: zymogen enzyme Isozyme: catalyze the same reaction with different physical properties LDH(1-5): lactate pyruvate LDH1-heart LDH5- skeletal muscle,Kinetics of enzymatic reaction,S influences the rate of reaction Michaelis-me

6、nten equation,Km unit equals to substrate unit with mol/L,1913年Michaelis和Menten提出反应速度与底物浓度关系的数学方程式，即米曼氏方程式，简称米氏方程式(Michaelis equation)。,S：底物浓度 V：不同S时的反应速度 Vmax：最大反应速度(maximum velocity) m：米氏常数(Michaelis constant),米-曼氏方程的推导,米曼氏方程式推导基于两个假设： E与S形成ES复合物的反应是快速平衡反应，反应速度取决于慢反应ES分解为E及P。即 Vk3ES (1) S的总浓度远远大于E

7、的总浓度，在反应的初始阶段，S的浓度可认为不变。 即 SSt,米-曼氏方程的推导,稳态：是指ES的生成速度与分解速度相等，即 ES恒定。 K1 (EtES) SK2 ES + K3 ES,米-曼氏方程的推导,则(2)变为: (EtES) S Km ES,米-曼氏方程的推导,当底物浓度很高，将酶的活性中心全部饱和时，即EtES，反应达最大速度 VmaxK3ESK3Et (5),将(5)代入(4)得米氏方程式：,米-曼氏方程的推导,S influences the rate of reaction,The significance of Km Km=Sv=V/2（mol/L） One enzyme

8、 has different Km to different substrate Natural substrate: the lowest Km, the fastest velocity Km is a characteristic constant E, S, Buffer Km reflects the affinity of enzyme to substrate The lower the Km, the greater the affinity,Km and Vmax determination,The Double-Reciprocal Plot,Kinetics of enz

9、ymatic reaction,E influences the rate of reaction,Kinetics of enzymatic reaction,T influences the rate of reaction,Kinetics of enzymatic reaction,pH value influences the rate of reaction,Kinetics of enzymatic reaction,Influences of inhibitors on the activity Irreversible inhibition E-SH: Hg2+ Ag+ As

10、(BAL) E-Ser: Organophosphorus pesticide cholinesterase Reversible inhibition Competitive inhibition Non-competitive inhibition Uncompetitive inhibition,Reversible inhibition,Competitive inhibition,Competitive inhibition,定义: 抑制剂与底物的结构相似，能与底物竞争酶的活性中心，阻碍酶底物复合物的形成，使酶的活性降低。 反应模式：,Characteristic of compet

11、itive inhibition,I和S具有结构相似性，争夺酶的活性中心 I存在时影响酶与底物结合，表观Km随I增加而增加 抑制作用的强度取决于I与E的相对亲和力及S和I比。与I 成正比；与S成反比。S极大时抑制作用解除。 Vmax不变,双倒数动力学方程： 1 Km I 1 1 V Vmax Ki S Vmax 双倒数作图： Vmax不变 表观Km增加,Kinetics of competitive inhibition,Case of competitive inhibition,Case of competitive inhibition,Reversible inhibition,Non

12、-competitive inhibition,Non-competitive inhibition,定义：抑制剂不与底物竞争酶的活性中心，而是与活性中心以外的必需基团相结合，使酶的构象改变而失去活性 反应模式：,Characteristic of non-competitive inhibition,抑制剂结合酶活性中心外必需基团， I既可结合E，也可结合ES。 I不影响S与E的结合（表观Km不变） ESI不能转变成产物 抑制作用只与I成正比（V 随I增加而增加） 。与底物浓度无关（Vmax）,Kinetics of non-competitive inhibition,Reversible

13、 inhibition,Uncompetitive inhibition,Uncompetitive inhibition,定义：抑制剂仅与酶-底物复合物(ES)结合，使酶失去催化活性 反应模式：,Characteristic of uncompetitive inhibition,I只能结合ES，不结合E ，S与E的结合有利于I的结合。 ESI不能生成产物， I 存在时ES，V I 存在增加E与S的亲和力（表观Km） 抑制作用只与I成正比而与底物浓度无关（Vmax）,Kinetics of uncompetitive inhibition,各种可逆抑制作用的比较,Influences of

14、activators on the activity,Essential activator Cofactors such as metal ions are usually activators of enzymes (Mg2+, Cu2+, Zn2+) Non-essential activator Cl-_ salivary amylase,Nomenclature of enzymes,Customary nomenclature of enzyme Systematic nomenclature of enzyme,Classification of enzyme,Six class

15、ws of enzyme defined: Oxidoreductases Transferases Hydrolases Lyases Isomerases ligases,The activity of enzyme is measured in IU,international unit (IU): the amount of enzyme produce 1umol of product per minute under particular conditions Commercial enzyme usually given in IU/mg Kat: the amount of e

16、nzyme produce 1mol of product per second under particular conditions 1Kat = 6E07 IU,Enzyme and medicine,In body, all physiological processes occur in an order, regulated manner and homeostasis is maintained. Both the amount or the regulation of enzyme taken accident, the health must be disturb. The

17、study of enzymes has immerse practical importance.,Enzyme and medicine,Based on Biochemistry The characteristic of health: normal metabolism Almost all of metabolisms involved in Enzyme reaction The characteristic of diseases: abnormal metabolisms Most of diseases from the abnormal metabolisms,Enzyme and medicine,Enzyme and disease Diseases about the key enzyme absence (genetic diseases such as gene mutation),苯丙氨酸羟化酶缺乏-PKU,酪氨酸酶缺陷白化病,Enzyme and medicine,Enzyme and disease,78年美国人民圣殿教900集体自杀,朱令铊中毒,Enzyme and medicine,Enzyme