※ 引述《AppleAmily ()》之铭言： : ※ 引述《elelith (trapped)》之铭言： : : 这题是有关suicide substrate的 : : Thre reaction scheme is : : K1 K2 : : E+S <----> ES ----> ED : : K' : : In this case [Et]-[ED] = [E] + [ES], where [Et] is the initail starting conc. : : of enzyme, [ED] is the conc. of dead enzyme, and [E] and [ES] are the conc. of : : viable enzyme that are repectively free and substrate-bound. : : a) Using the steady state approximation for [ES], derive an expression for the : : rate of creation of [ED]. (d[ED]/dt) : : d[ES]/dt= K1[E][S] - K'[ES] - K2[ES] = 0 : : [ES] = K1[E][S]/(K'+K1) : : d[ED]/dt = K2 [ES] 这样不知道对不对 跟d[ES]/dt好像没关系 ￣ー￣； : : 第二题跟第三题问在什麽时候 d[ED]/dt会是fist order and zeroth order in [S] : : first order when [S] is at low conc. and zeroth when [S] > [E]? : : when the rate of production of [ED] is zeroth in [S], what will be the rate? : : K2[ES]? : : 上面答案如果不对的还烦请指正Orz : : 谢谢 : first of all, in part a) you need to eliminate the term [ES] by substituting : the expression [ES] = K1[E][S]/(K'+K2) into d[ED]/dt = K2 [ES] since ES is : an intermediate of which the actual concentration cannot be measured. : the rate of formation for the product [ED] then becomes: : d[ED]/dt = K1K2[E][S]/(K'+K2) Well, for the first question, there was a hint I forgot to type out, it says the expression will contain the term {[Et]-[ED]} instead of the usual [Et] how and which term should I substitute with {[Et]-[ED]}? : when the rate is zeroth order with respect to [S], the expression becomes : d[ED]/dt = K1K2[E]/(K'+K2) : for the second question....I am not really sure if your answer is right or : not since you didn't provide with any justification, but, generally, I would : assume the rate of the enzyme catalyzed reaction to be zeroth order with : respect to [S] if the concentration of the substrate is large comparing to : [E] (thus can be assumed constant throughout the reaction); the rate should : be 1st order with respect to [S] in all other cases according to the kinetics. thx for your reply -- something's missing --

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