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1、Chapter 4 Chemistry of Enzyme 酶化学,主要介绍酶的化学本质、结构和特性；酶的作用动力学；酶的作用机理；酶的应用；还介绍了别构酶、共价调节酶、同工酶等的概念、性质、生物学意义。,Section1 What is enzymes,Enzymes are catalysts that increase the rate of chemical reaction without being changed themselves in the process. 酶是一类能加快化学反应速度而在反应过程中自身不发生改变的催化剂,C6H12O6 + 6O26CO2+6H2O+28
2、70kJ of energy,1. What difference compare to chemical catalysts,Catalytic power 高催化效率 Specificity 高度专一性 Regulation 活性受调节,Catalytic power 高催化效率,Enzymes display enormous catalytic power, accelerating reaction rates as much as 1016 over uncatalyzed levels, which is far greater than any synthetic cataly
3、sts can achieve, and enzymes accomplish these astounding feats in dilute aqueous solution under mild conditions of temperature and pH.,For example,H2N- CO- NH2 + 2H2O + H+ 2NH4+ + HCO3- urea At 20, k of enzyme-catalyzed reaction is: 3104/sec k of uncatalyzed reaction is: 310-10/sec,（一）命名,1系统名称（syste
4、matic name）,（1）标明底物，催化反应的性质,G-6-PF-6-P G-6-P异构酶,例:,系统名称包括底物名称、构型、反应性质，最后加一个酶字。,2. Enzyme nomenclature,Substrate(s) : reaction type 草酸:氧氧化酶,（2）两个底物参加反应时应同时列出，中间用冒号（:）分开。如其中一个底物为水时，水可略去。,例1： 丙氨酸+-酮戊二酸 谷氨酸+丙酮酸,丙氨酸:-酮戊二酸氨基转移酶,例2： 脂肪+H2O 脂酸+甘油,脂肪水解酶,2习惯名称（recommended name）,（1）底物,（2）反应性质,（3）底物，反应性质: 蛋白酶;淀
5、粉酶,（4）来源或其它特点: 脲酶;胃蛋白酶, 胰蛋白酶,（二）系统分类法及编号,1分类:,6大类酶，氧转水 裂异连,2编号:,用4个阿拉伯数字的编号表示，数字中用“”隔开，前面冠以EC（为Enzyme Commission）。,EC 类.亚类.亚亚类.排号，如EC l.1.1.1,Classification 分类 The enzyme commission defined all enzymes as six groups. Oxidoreductases 氧化还原酶 Transferases 转移酶 Hydrolases 水解酶 Lyases 裂解酶 Isomerases 异构酶 Lig
6、ases 连接酶,Numbering 序号 Catalyze oxidation-reduction reaction Acting on CH-OH group of donor E.C. 1. 1. 1. 1 With NAD or NADH as acceptor The reaction it catalyzes,3. The chemical nature 化学本质,Enzymes are proteins Evidences: Unstable to heat 对热不稳定 Amphiphic 两性性质 Denaturation 变性 Colloidal properties 胶体性
7、质 Crystalization 可被结晶 Amino acid sequence 氨基酸序列分析,Ribozyme 核酶 1981-1982, Thomas R. Cech discovered a natural rRNA segment which had the activity to catalyze itself during the splicing process of precursor. Then, a L19 RNA with enzyme-like activity and other RNAs were found.,Thomas Cech University of
8、 Colorado at Boulder, USA,1983年美国S.Altman等研究RNaseP（由20%蛋白质和80%的RNA组成），发现RNaseP中的RNA可催化E. coli tRNA的前体加工。,Sidney Altman Yale University New Haven, CT, USA,Cech和Altman各自独立地发现了RNA的催化活性，并命名这一类酶为ribozyme（核酶），2人共同获1989年诺贝尔化学奖。,1Cell vol 31, 147157，1982年。,2Sci. Amer. Vol 255, 6475，1986。,有些DNA也有催化活性,1995年Cu
9、enoud等发现有些DNA分子亦具有催化活性。,抗体酶（abzyme）,抗体：与抗原特异结合的免疫球蛋白。,抗体酶：指具有催化功能的抗体分子，在抗体分子的可变区 （即肽链的N端）是识别抗原的活性区域，这部分区域被赋予了酶的属性。,抗体酶的性质,抗体酶的用途,半抗原,4. Composition of enzymes,(1) Simple enzyme（单纯酶）. Contain only amino acids. (2) Conjugated enzyme（结合酶）. A simple protein (apoenzyme脱辅基酶) combined with a non- protein c
10、omponent (prosthetic group辅基, cofactor or coenzyme 辅酶或辅因子). Holoenzyme=apoenzyme+ cofactor(s) 全酶 = 酶蛋白 + 辅因子,5. Coenzyme and cofactor,Coenzyme 辅酶: a complex organic molecule Cofactor辅因子: inorganic ions Coenzyme: loose conjugate with protein, can be released by dialysis. Prosthetic group辅基: tide conj
11、ugate with protein, can not be released by dialysis透析. Specific coenzyme: necessary for the activity. General coenzyme: can combine to different enzymes to form similar function.,6. Monomer, oligomer and complex,Monomer单体酶: consists of one polypeptide Oligomer寡聚酶: consists of two or more polypeptide
12、s Enzyme complex多酶复合体: consists of 2-6 functional related enzymes,7. Structure related to function,Active sites and essential groups Active site活性中心: the region that binds the substrates and converts it into product. It is usually a relatively small part of the whole enzyme molecule and is a three-d
13、imensional entity 实体 formed by amino acid residues that can lie far apart in the linear polypeptide chain.,Essential groups必需基团: the groups related to the activity of enzyme. Binding groups结合基团: to combine the substrate. Catalytic groups催化基团: to catalyze the substrate. in most cases binding group an
14、d catalytic group are separated groups. Occasionally, the same group can play the roles of binding and catalysis. All groups in active site are essential groups. Some groups beyond the active site can be also the essential groups.,The substrate-binding pockets of trypsin, chymotrypsin, and elastase,
15、Enzyme-substrate interactions at six sugar residue-binding subsites of the lysozyme active site,8. Activation of zymogens,zymogen酶原激活: the precursor of enzyme without activity（没有活性的前体）. These always happen in the hydrolytic enzymes related digestion（消化相关水解酶）. Zymogen can be activated when it is secr
16、eted to the place where they plays the roles. The activating usually is a course of splicing（拼接过程）.,Activating of chymotrypsinogen into active chymotrypsin,9. Isoenzymes 同工酶,Isoenzymes or isozymes are different forms of an enzyme which catalyze the same reaction, but exhibit different physical or kinetic 动力学properties, such as isoelectric point, pH optimum, substrate affinity or effect of inhibitors. Different isozyme forms of a given enzyme are usually derived
