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Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

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10.1 <strong>Kinetics</strong> of enzyme catalyzed reactions (homogeneous catalysis) 215<br />

10.1.1 The Michaelis-Menten mechanism<br />

Basic reaction scheme:<br />

E+S 1<br />

À ES (10.2)<br />

−1<br />

ES 2<br />

→ E+P (10.3)<br />

Typical values of 2 :<br />

2 ≈ 10 2 10 3 s −1 (in some cases up to 10 6 s −1 ) (10.4)<br />

Reaction rate:<br />

[P]<br />

<br />

= − [S]<br />

<br />

= 2 [ES] (10.5)<br />

[ES]<br />

<br />

= 1 [E] [S] − −1 [ES] − 2 [ES] (10.6)<br />

≈ 0 (10.7)<br />

Mass balance:<br />

Steady state ES concentration:<br />

[E] 0<br />

= [E]+[ES] (10.8)<br />

y [E] = [E] 0<br />

− [ES] (10.9)<br />

[S] 0<br />

= [S]+[ES]+[P] (10.10)<br />

y [S] = [S] 0<br />

− [ES] − [P] (10.11)<br />

[ES]<br />

<br />

= 1 ([E] 0<br />

− [ES]) ([S] 0<br />

− [ES] − [P]) − ( −1 + 2 )[ES] (10.12)<br />

≈ 0 (10.13)<br />

Approximations:<br />

y<br />

[ES]<br />

<br />

[E] 0<br />

¿ [S] 0<br />

(10.14)<br />

[ES] ¿ [S] 0<br />

(10.15)<br />

[P] ≈ 0 for early times (10.16)<br />

= 1 [E] 0<br />

[S] 0<br />

− 1 [S] 0<br />

[ES] − ( −1 + 2 )[ES] (10.17)<br />

≈ 0 (10.18)<br />

Steady state ES concentration:<br />

[ES] <br />

=<br />

1 [E] 0<br />

[S] 0<br />

1 [S] 0<br />

+ −1 + 2<br />

(10.19)

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