河南师范大学：《生物化学》课程PPT教学课件（英文版）Section C Enzymes

C Enzymes C1 Introduction to enzymes C2 Thermodynamics热力学 C3 Enzyme kinetics动力学 C4 Enzyme inhibition C5 Requlation of enzyme activity

• C1 Introduction to enzymes • C2 Thermodynamics热力学 • C3 Enzyme kinetics动力学 • C4 Enzyme inhibition • C5 Regulation of enzyme activity C Enzymes

C1 Introduction to enzymes Enzyme as catalysts催化剂 Active site活性部位 Substrate specificity底物专一性 ° Enzyme classification分类 Enzyme assays酶的测定 Linked enzyme assays Coenzymes辅酶 and prosthetic groups辅基 Isoenzymes同工酶

• Enzyme as catalysts催化剂 • Active site 活性部位 • Substrate specificity底物专一性 • Enzyme classification分类 • Enzyme assays酶的测定 • Linked enzyme assays • Coenzymes辅酶 and prosthetic groups辅基 • Isoenzymes同工酶 C1 Introduction to enzymes

Enzymes as catalysts Enzymes are catalysts that change the rate of a reaction without being changed themselves Enzyme catalyzed reactions usually take place under relatively mild conditions(T, P,pH) Enzymes are highly specific and their activity can be requlated Virtually all enzymes are proteins, although some catalytically active RNAs have been identified

Enzymes as catalysts ➢ Enzymes are catalysts that change the rate of a reaction without being changed themselves ➢ Enzyme catalyzed reactions usually take place under relatively mild conditions(T,P,pH). ➢ Enzymes are highly specific and their activity can be regulated. ➢ Virtually all enzymes are proteins, although some catalytically active RNAs have been identified

Active site活性部位 Active site is the region that binds the substrate i and converts it into product 结合部位:负责与底物的结合,决定酶的专一性。 催化部位:负责催化底物键的断裂形成新键,决定酶的催 化能力。 Smal(1-2%)、 a three- dimensional entity实体 Cleft or crevice裂缝 on the surface of enzyme Bind by multiple weak forces Enzyme-substrate complex transition state complex过渡态复合物- product

Active site活性部位 • Active site is the region that binds the substrate 底物 and converts it into product。 • 结合部位：负责与底物的结合，决定酶的专一性。 • 催化部位：负责催化底物键的断裂形成新键，决定酶的催 化能力。 • Small（1-2%）、a three-dimensional entity实体 • Cleft or crevice裂缝on the surface of enzyme • Bind by multiple weak forces • Enzyme-substrate complex • transition state complex过渡态复合物--→product

Active site

Active site Active site

B

Uracil (from substrate) Threonine side chain serine e side chain FIGURE 8.8 Hydrogen bonds between an enzyme and substrate. The enzyme ribonuclease forms hydrogen bonds vith the uridine component of the substrate

nzyme-substrate complex Tyr 96 PeAYOYeY Phe 87 va|247 Asp 297 Leu 244 Camphor(substrate) va|295 Heme FIGURE 8.5 Structure of an enzyme-substrate complex(Left) The enzyme cytochrome P-450 is illustrated bound to its substrate camphor. (Right) In the active site the substrate is surrounded by residues from the enzyme. Note also the presence of a heme cofactor

Enzyme-substrate complex

Two models -enzyme bind its substrate Lock and key model锁-钥: Emil Fischer,1894 · Induced fit model诱导契合: Danie|E Koshland jr 1958

Two models---enzyme bind its substrate • Lock and key model锁-钥:Emil Fischer,1894 • Induced fit model诱导契合:Daniel E. Koshland,Jr 1958

Lock and key model Substrate b Active site ES complex Enzyme

Lock and key model