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Enzyme Inhibition (Mechanism)
Competitive Non-competitive Uncompetitive E Substrate E X Cartoon Guide Compete for active site Inhibitor Different site E + S → ES → E + P + I ↓ EI ← ↑ E + S → ES → E + P I I ↓ ↓ EI + S →EIS ← ↑ E + S → ES → E + P + I ↓ EIS ← ↑ Equation and Description 酵素 的抑制劑有不同的抑制機制，通常依照抑制劑對酵素的結合方式，可分成兩大類。其一為競爭同一活性區 (competitive)，可以用提高基質濃度的方法來競爭；另一則是結合在活性區之外的地方，又可分成 non-competitive 及 uncompetitive 兩種。後面兩種抑制方式大致相同，因此有些課本也就不再細分，其差別在於基質的結合，會不會影響抑制劑的結合。雖然這幾種抑制方式，都是可逆反應，但只有 competitive 可以用提高基質的方式來對抗抑制。 [I] binds to free [E] only, and competes with [S]; increasing [S] overcomes Inhibition by [I]. [I] binds to free [E] or [ES] complex; Increasing [S] can not overcome [I] inhibition. [I] binds to [ES] complex only, increasing [S] favors the inhibition by [I]. Juang RH (2004) BCbasics
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Enzyme Inhibition (Plots)
Competitive Non-competitive Uncompetitive Vmax Vmax Km [S], mM Vmax [S], mM vo vo Direct Plots Double Reciprocal Vmax’ I Km’ Vmax’ I I Km Km Km’ [S], mM = Km’ Vmax unchanged Km increased Vmax decreased Km unchanged Both Vmax & Km decreased 1/[S] 1/Km 1/vo 1/ Vmax I 1/vo 1/ Vmax 1/[S] 1/Km 1/[S] 1/Km 1/ Vmax 1/vo I Intersect at X axis I Two parallel lines Intersect at Y axis 這些 抑制機制都可以用酵素動力學來描述，使用雙倒數作圖更可明顯地指出是屬於何種抑制方式。不過，以上三種作圖都是屬於最典型者，很多時候實驗所得到的作圖結果，可能會有混合型態出現，則是較為複雜的抑制機制，或者有其他的干擾因子在內。 Juang RH (2004) BCbasics
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