2.The active site is a three-dimensional entity formed by groups that come from different parts of the linear amino acid sequence Figure 8-11 (A)Space-filling model of lysozyme. Two catalytically critical residues are shown in red and green.Several other residues in the active site are shown in yellow.(B)Schematic diagram of lysozyme showing that the active site is formed by residues that come from different segments of the polypeptide chain.[(A)Drawn from 6lyz.R. -H3N- C00 Diamond./Mol.Biol.82(1974):371.] 355262. 101108129 63
Active site The active site is the region of the enzyme that binds the substrate, to form an enzyme-substrate complex, and transforms it into product. The active site is a three-dimensional entity, often a cleft or crevice on the surface of the protein, in which the substrate is bound by multiple weak interactions
Active site The active site is the region of the enzyme that binds the substrate, to form an enzyme-substrate complex, and transforms it into product. The active site is a three-dimensional entity, often a cleft or crevice on the surface of the protein, in which the substrate is bound by multiple weak interactions
三、研究酶活性中心的方法 1.物理学方法： 用X射线衍射法直接检测底物或其类 似物与酶形成的中间复合物（包括酶和 底物）的相对位置
三、研究酶活性中心的方法 1.物理学方法： 用X射线衍射法直接检测底物或其类 似物与酶形成的中间复合物（包括酶和 底物）的相对位置
2.化学修饰法：根据所用修饰试剂不同，分为 1)非专一性化学修饰 用非专一性的修饰试剂与氨基酸侧链基团作用。 若某基团被修饰后： 酶活性不变——该基团可能不是酶的必需基团 酶活性降低或丧失——该基团可能是酶的必需基团 但不能确定化学试剂是同活性中心内的必需基团结合
2.化学修饰法：根据所用修饰试剂不同，分为 1)非专一性化学修饰 用非专一性的修饰试剂与氨基酸侧链基团作用。 若某基团被修饰后： 酶活性不变——该基团可能不是酶的必需基团 酶活性降低或丧失——该基团可能是酶的必需基团 但不能确定化学试剂是同活性中心内的必需基团结合
活性中心基团的鉴定标准 ①失活程度与修饰剂浓度成一定比例关系。 ②S或可逆抑制剂有保护作用（活性中心）。 先加S或竞Ⅰ 加共价修饰剂 透析除去S 或竞Ⅰ 活性不丧失
活性中心基团的鉴定标准 ①失活程度与修饰剂浓度成一定比例关系。 ②S或可逆抑制剂有保护作用（活性中心）。 先加S或竞Ⅰ 加共价修饰剂 透析除去S 或竞Ⅰ 活性不丧失