生物化学 习题课二.pptVIP

糜蛋白酶的一级结构及其激活过程如图所示，这个激活顺序能否颠倒？给出理由。2.Lysozymedestroysthecellwallofbacteriabycatalyzingthehydrolysisof1,4-β-linkagesbetweenN-acetylmuramicacid(NAM)andN-acetyl-D-glucosamine(NAG)residuesinapeptidoglycan.Sixhexosesofthesubstratefitintotheactivesiteoflysozyme,adeepcleftacrosspartoftheglobularproteinsurfacethiscleft.FigureAshowsthehydrolyticprocessof1,4-β-linkagesbetweenNAMandNAGandfigureBshowsthepH-activityprofileoflysozyme.PleasecalculatetheratiooftheenzymemoleculeswhichreallyworkatpH3.8,5.2,6.6toallenzymemolecules,andexplainfigureBaccordingtoyourcalculation(pH=pKa+lg([A-]/[HA])；pKaGlu=5.9,pKaAsp=4.5；102.1≈126，100.7≈5).AB1．pH3.8lg([Asp-]/[HAsp])＝pH–pKa＝3.8–4.5=-0.7，[Asp-]/[HAsp]＝1/5起碱作用的Asp所占比例[Asp-]/（[HAsp]＋[Asp-]）＝[Asp-]/（5[Asp-]＋[Asp-]）＝1/6同理，lg([Glu-]/[HGlu])＝3.8–5.9＝-2.1，[Glu-]/[HGlu]＝1/126起酸作用的Glu所占比例[HGlu]/（[HGlu]＋[Glu-]）＝[HGlu]/（[HGlu]/126＋[HGlu]）＝126/127真正能工作的酶分子比例＝（1/6）×（126/127）≈16.5%2.pH5.2类似1的计算，此时真正能工作的酶分子比例＝（5/6）×（5/6）≈69.4%3.pH6.6类似1的计算，此时真正能工作的酶分子比例＝（126/127）×（1/6）≈16.5%此计算说明，反应体系pH值的变化影响作为催化基团GLu35和Asp52的解离状态，从而影响酸碱催化和共价催化。要使溶菌酶保持高活性，需要一个恰当的pH值-----所谓最佳催化pH值。3.Youareworkingonacompoundasapotentialdrugthatinhibitsanoverproducedenzymewhoseuncontrolledactivityleadstouncontrolledcellproliferation(cancer).Asteady-statekineticanalysisoftheenzyme-catalyzedreactionwascarriedout,withvelocitiesmeasuredasafunctionoftheconcentrationofthesubstrateintheabsenceandinthepresenceof10nMinhibitor.Theresultsofthekineticsexperimentareplottedforyoubelow.Pleaseanswerthefollowingquestions.Whattypeofinhibitoristhiscompound(beasspecificasyoucan)?Showthediagramoftheinhibitor’smechanism(byEdenotingenzyme,Sdenotingsubstrate,Idenotinginhibitor).CalculatetheKm,KcatintheabsenceofinhibitorandKmapp,Kcatappinthepr