Biological catalysts Typically are very large proteins. e Permit reactions to 'go at conditions that the body can tolerate. Can process millions of molecules every second Are very specific -react with one or only a few types of molecules(substrates)
Introduction to enzymes Consider the following reaction 2H2O2=2H2O+O2 The reaction is thermodynamically favored but occurs very slowly. Slow reaction rate is due to the high activation energy for the reaction Only a small portion of the molecules have sufficient energy to overcome this energy. We could increase the energy of the system but this is not an option for biological systems
三、酶的化学本质及其组成 (一)酶的化学本质 酶的化学本质除有催化活性的RNA之外几 乎都是蛋白质。 注意:不能说所有的蛋白质都是酶,只是 具有催化活性的蛋白质才称酶 (二)酶的化学组成 从化学本质来看,酶可以分为 1.单纯蛋白质( simple protein) 2.缀合蛋白质( conjugated protein)
（一）酶的化学本质 酶的化学本质除有催化活性的RNA之外几 乎都是蛋白质。 注意：不能说所有的蛋白质都是酶，只是 具有催化活性的蛋白质才称酶。 （二）酶的化学组成 从化学本质来看，酶可以分为： 1. 单纯蛋白质（simple protein） 2. 缀合蛋白质（conjugated protein） 三、酶的化学本质及其组成
缀合蛋白质(全酶)=蛋白质(脱辅酶, a coenzyme或 apoprotein)+辅助因子 (cofactor 辅助因子是指一些对热稳定的非蛋白质小 分子物质或金属离子,包括: (1)辅酶( coenzyme):与脱辅酶结合比较松 弛的小分子有机化合物,通过透析方法即可出 去,如辅酶I等。 (2)辅基( cofactor):以共价键和脱辅酶结 不能通过透析出去
缀合蛋白质（全酶）=蛋白质（脱辅酶， apoenzyme或apoprotein）+辅助因子 （cofactor） 辅助因子是指一些对热稳定的非蛋白质小 分子物质或金属离子，包括： （1）辅酶（coenzyme）：与脱辅酶结合比较松 弛的小分子有机化合物，通过透析方法即可出 去，如辅酶Ⅰ等。 （2）辅基（cofactor）：以共价键和脱辅酶结 合，不能通过透析出去
12-2 Enzymes 2 Most are proteinsexcept small group of catalyticRNAs) Provide a specific environment in which a given reaction energetically more favorable Catalytic activity depends onintegrity of their native conformation Some enzymes require no chemical groups for activity other than their owta Some enzymes require additionatofactorsfor activity inorganic ions eg. Fe2+ or 3+, Mg2+ Mn2+, Zn2+ complex organic molecule =coenzyme, which can serve as transient carriers of electrons or specific functional groups both coenzymeand one or more metal ions a coenzyme +/-metal ion that is very tightly bound to an enzyme a prosthetic group Activity of many enzymes isregulated Many named by adding suffix ase to the name of their substrate or a word describing their activity