Kcat KM Values:catalytic efficiency催化效率 TABLE 8.7 I Enzymes for which kcat/Km is close to the diffusion-controlled rate of encounter Enzyme kcat/KM (s-1M-1) Acetylcholinesterase 1.6×108 Carbonic anhydrase 8.3×107 Catalase 4×107 Crotonase 2.8×108 Fumarase 1.6×108 Triose phosphate isomerase 2.4×108 B-Lactamase 1×108 Superoxide dismutase 7×109 Source:After A.Fersht,Structure and Mechanism in Protein Science:A Guide to Enzyme Catalysis and Protein Folding (W.H. Freeman and Company,1999),Table 4.5. 上述酶Kca/Ky ratios已达完美极限，催化速度仅受溶液扩 散速度的限制
kcat / KM Values: catalytic efficiency 催化效率 上述酶kcat/KM ratios已达完美极限，催化速度仅受溶液扩 散速度的限制
TABLE 8.6 Substrate preferences of chymotrypsin Amino acid in ester Amino acid side chain kcat/KM (s-1M-1) Glycine -H 1.3×10-1 CH3 Valine -CH 2.0 CH3 Norvaline -CH,CH,CH3 3.6×102 Norleucine -CH,CH,CH.CH3 3.0×103 Phenylalanine CH2 1.0×105 Source:After A.Fersht,Structure and Mechanism in Protein Science:A Guide to Enzyme Catalysis and Protein Folding(W.H.Freeman and Company,1999),Table 7.3
Most Biochemical Reactions Include Multiple Substrates A+BP+Q Many such reactions transfer a functional group,such as a phosphoryl or an ammonium group,from one substrate to the other.In oxidation-reduction reactions,electrons are transferred between substrates.(主要是转移反应及氧化 还原反应) (1)Sequential Reactions序列反应 -ordered sequential mechanism有序的序列反应机制 -random sequential mechanism随机的序列反应机制 (2)Double-Displacement(Ping-Pong)Reactions乒乓反应
Most Biochemical Reactions Include Multiple Substrates A + B P + Q Many such reactions transfer a functional group, such as a phosphoryl or an ammonium group, from one substrate to the other. In oxidation-reduction reactions, electrons are transferred between substrates. (主要是转移反应及氧化 还原反应） (1)Sequential Reactions 序列反应 - ordered sequential mechanism 有序的序列反应机制 - random sequential mechanism 随机的序列反应机制 (2) Double-Displacement (Ping-Pong) Reactions 乒乓反应
(1)Sequential Reactions:ordered sequential mechanism 有序序列机制 Sequential Reactions:a ternary complex of the enzyme and both substrates forms.所有底物都可结合到酶上，然后 再形成产物 Ordered:the substrates bind the enzyme in a defined sequence. +NADH+Ht三HO—C—H+NAD* CH3 CH3 Pyruvate Lactate 乳酸脱氢酶，结合底物是有序的、释放产物也是有序的。The enzyme exists as a ternary complex:first,consisting of the enzyme and substrates and,after catalysis,the enzyme and products. NADH Pyruvate Lactate NAD+ Enzyme Enzyme E(NADH)(pyruvate) E(lactate)(NAD+)
(1) Sequential Reactions： ordered sequential mechanism 有序序列机制) Sequential Reactions: a ternary complex of the enzyme and both substrates forms. 所有底物都可结合到酶上，然后 再形成产物 Ordered: the substrates bind the enzyme in a defined sequence. 乳酸脱氢酶，结合底物是有序的、释放产物也是有序的。The enzyme exists as a ternary complex: first, consisting of the enzyme and substrates and, after catalysis, the enzyme and products
(1)Sequential Reactions:Random sequential mechanism The order of the addition of substrates and the release of products is random. creatine kinase(肌氨酸激酶) NH2 NH. + 0 CNH2+ATP 0 ADP CH3 CH3 肌肉的重要能源 Creatine Phosphocreatine ATP Creatine Phosphocreatine ADP Enzyme- Enzyme E(creatine) E(phosphocreatine) (ATP) (ADP) Creatine ATP ADP Phosphocreatine
(1) Sequential Reactions： Random sequential mechanism The order of the addition of substrates and the release of products is random. creatine kinase(肌氨酸激酶) 肌肉的重要能源