Induced fit model Substrate c ES complex Enzyme FIGURE 8. 10 Induced-fit model of enzyme-substrate binding. In this model, the enzyme changes shape on substrate binding. The active site forms a shape complementary to the substrate only after the substrate has been bound
Induced fit model
Induced fit model Substrates Product Enzyme Enzyme-substrate Enzyme complex Active sites in the uninduced enzyme are shown schematically with round contours. Binding of the first substrate(gold)induces a conformational shift(angular contours) that facilitates binding of the second substrate(blue), with far lower energy than otherwise required. When catalysis is complete, the product is released, and the enzyme returns to its uninduced state
Induced fit model • Active sites in the uninduced enzyme are shown schematically with round contours. Binding of the first substrate (gold) induces a conformational shift (angular contours) that facilitates binding of the second substrate (blue), with far lower energy than otherwise required. When catalysis is complete, the product is released, and the enzyme returns to its uninduced state
Substrate specificity Substrate specificity is often determined by changes in relatively few amino acids in the active site 结构专一性 1)绝对专一性(脲酶); 2)相对专一性(酶作用于一类结构相近的底物) 立体异构专一性 1)旋光异构专一性(L氨基酸氧化酶) 2)几何异构专一性
Substrate specificity • Substrate specificity is often determined by changes in relatively few amino acids in the active site. • 结构专一性： 1) 绝对专一性（脲酶）； 2) 相对专一性（酶作用于一类结构相近的底物） • 立体异构专一性 1) 旋光异构专一性（L-氨基酸氧化酶） 2) 几何异构专一性
Serine proteases丝氨酸蛋白酶家族 Trypsin胰蛋白酶 cleaves on the carboxyl side of positively charged Lys or Arg residues Chymotrypsin胰凝乳蛋白酶: cleaves on the carboxyl side of bulky aromatic and hydrophobic amino acid residues E| astate弹性蛋白酶: cleaves on the carboxyl side of small uncharged side chains
Serine proteases丝氨酸蛋白酶家族 • Trypsin胰蛋白酶 cleaves on the carboxyl side of positively charged Lys or Arg residues. • Chymotrypsin 胰凝乳蛋白酶: cleaves on the carboxyl side of bulky aromatic and hydrophobic amino acid residues • Elastase 弹性蛋白酶: cleaves on the carboxyl side of small uncharged side chains
Asp 189 Val 190 Va|216 Val 190 va|216 Asp 189 Chymotrypsin Trypsin Elastase FIGURE 9.13 The St pockets of chymotrypsin, trypsin, and elastase. Certain residues play key roles in determining the specificity of these enzymes. The side chains of these residues, as well as those of the active- site serine residues, are shown in color