中南大学 生物化学 考研课件 ch15 酶的特性和调控 enzyme specificity and regulation

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1、BiochemistryForSpecialityofBiotechnologyorBioengineeringatCSUMr.XIAJinlanContentsEnzymespecificity(self-study)酶的特异性(自学)The“lockandkey”hypothesis锁钥假设The“inducedfit”hypothesis诱导契合假设ControlofenzymeactionControlofenzymeamount酶量的控制Controlofenzymeactivity酶活性的控制EnzymespecificitySpecificityist

2、heresultofmolecularrecognitionThe“lockandkey”hypothesisThe“inducedfit”hypothesisTherearetwomodelsofbindingofasubstratetoanenzymeLock-and-keymodel锁和钥匙模型Founder:EmilFisher,1894PrincipleShapeofthesubstrateandtheactivesiteoftheenzymearerigidandfixed,theyfittogetherlikeakeyintoitslockInduce

3、d-fitmodel诱导-契合模型Founder:DanielE.,KoshlandJr.,1958PrincipleBindingofsubstrateinducesaconformationalchangeintheactivesiteofenzyme.Enzymemaydistortthesubstrate,forcingitintoaconformationsimilartothatofthetransitionstate.Theinducedfitmodel(ex.ofhexokinase)BeforeglucosebindingAfterglucoseb

4、indingSubstrateishighlyspecifictoitsenzymeThespecificitybetweenenzymeanditssubstratedependsonthepropertiesandspatialarrangementoftheaminoacidresiduesformingtheactivesiteofanenzymeTypicalexampleSerineproteasesTrypsin胰蛋白酶:cleavesC-terminalsideofbasicaminoacidresidues(Arg,Lys)Chymotrypsin

5、胰凝乳蛋白酶:cleavesC-terminalsideofaromaticaminoacidresidues(Phe,Trp,Tyr)Elastase弹性蛋白酶(胰肽酶E)：cleavesC-terminalsideofsmallunchargedaminoacidresidues(Gly,Ala)Question:Pleasecomparethedifferenceinmechanismofspecificityamongtheserineproteasestrypsin,chymotrypsinandelastase.请比较丝氨酸胰蛋白酶、胰凝乳蛋白酶、弹性蛋

6、白酶在特异性机制的区别CarbamidineControlofenzymeactionControlofenzymeamountMainlybycontrollinggenetranscriptionControlslowlyControlofenzymeactivityBycontrollingpost-translation,i.e.,enzyme(structural)modificationControlfastFeedbackregulation反馈调控Reversiblenoncompetitiveinhibition可逆非竞争抑制Feedbackreg

7、ulationisusuallyaccompaniedbyAllostericaction反馈调控通常伴随着变构作用Reversiblecovalentmodification可逆共价修饰Themostcommon:Phosphorylationanddephosphorylation最典型:磷酸化和去磷酸化Irreversiblemodificationofproenzymes酶原的非可逆修饰Exampleofallostericcontrolandcovalentmodification变构调控和共价修饰的例子Controlofenzymeactivity(