lecture notes enzyme 3 inhibition kinetics web

Download Lecture Notes Enzyme 3 Inhibition Kinetics Web

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Inhibited Enzyme Kinetics Inhibitors may bind to enzyme and reduce their activity. Enzyme inhibition may be reversible or irreversible. For reversible enzyme inhibition, there are -

Inhibited Enzyme Kinetics Competitive inhibitors (I) - substrate analogs - compete with substrate for the active site of the enzymeK1

E+S+

K-1

k2 ES P E

I

KIEI

Inhibited Enzyme Kinetics Competitive inhibitors (I) Assume rapid equilibrium and with the definitions of

d[P] v k [ES] 2 dt k 1 [ E ][S ] ' Km k1 [ ES ][ E ][I ] KI [ EI ]

[E0 ] [E] [ES] [EI ]

Inhibited Enzyme Kinetics Competitive inhibitors (I), we can obtain,v Vm [ S ]

' (1 [ I ] / K ) [ S ] Km I

v

Vm [ S ] ' Km , app [ S ]

' ' (1 [ I ] / K ) Km K , app m I When [I] =0,

' ' Km K , app m

Vm Remains

that of Michaelis-Menten equation. .

K m ,app is

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I) - not substrate analogs - bind onKm

.

E+S+

k2 ES P E+

I KIKm

IKI ESI

EI+S

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I) Assume: - rapid equilibrium

- same equilibrium constants of inhibitor binding to E and ES KI- same equilibrium constants of substrate Km binding to E and EI

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I)

d[P] v k [ES] 2 dt k 1 [ E ][S ] [ EI ][S ] ' Km k1 [ ES ] [ ESI ][ E ][I ] [ ES ][I ] KI [ EI ] [ ESI ]

[E0 ] [E] [ES] [EI ] [ESI ]

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I) we can obtain,v Vm [ S ] ' [ S ]) (1 [ I ] / K I )(K m

Vm, app [ S ] v ' [S ] Km

K m remains

in Michaelis-Menten equation. .

Vm , app

is

Vm, app Vm /(1 [ I ] / K I ) When [I] =0,

Vm, app Vm

Inhibited Enzyme Kinetics Uncompetitive inhibitors (I) - have no affinity for - bind only to the Assume rapid equilibrium,Km

itself.

E+S

k2 ES P E+

I

KI ESI

Inhibited Enzyme Kinetics Uncompetitive inhibitors (I)

d[P] v k [ES] 2 dt k 1 [ E ][S ] ' Km k1 [ ES ][ ES ][I ] KI [ ESI ]

[E0] [E] [ES] [ESI]

Inhibited Enzyme Kinetics Uncompetitive inhibitors (I) we can obtain,v (Vm /(1 [ I ] / K I ))[S ] ' /(1 [ I ] / K )) [ S ] (K m I

Vm, app [ S ] v ' , app [ S ] Km ' ' /(1 [ I ] / K ) Vm, app Vm /(1 [ I ] / K I ) K m K , app m I

' ' K m, app / Vm, app K m / Vm Burk Plot

in Lineweaver-

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors - can cause inhibition at substrate concentration - bind only to the . Assume rapid equilibrium, Km k2 E+S ES P E+

S

K SI ES2

Substrate Inhibition

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors (I)

d[P] v k [ES] 2 dt k 1 [ E ][S ] ' Km k1 [ ES ][ ES ][S ] K SI [ ES 2]

[E0] [E] [ES] [ES2]

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors (I) we can obtain,v Vm [S ] ' [ S ] [S ]2 / K Km SI

At low substrate concentration [S ]2 / K

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