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

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Presentation transcript:

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 enzyme K1 E+S K-1 + I EI K I

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

Inhibited Enzyme Kinetics Competitive inhibitors (I), we can obtain, When [I] =0, Remains that of Michaelis-Menten equation. is.

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I) - not substrate analogs - bind on. E+S + I EI+S K I + I ESI K I Km’

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I) Assume: - rapid equilibrium - same equilibrium constants of inhibitor binding to E and ES K I - same equilibrium constants of substrate binding to E and EI Km’

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I)

Inhibited Enzyme Kinetics Noncompetitive inhibitors (I) we can obtain, When [I] =0, remains in Michaelis-Menten equation. is.

Inhibited Enzyme Kinetics Uncompetitive inhibitors (I) - have no affinity for itself - bind only to the. Assume rapid equilibrium, E+S + I ESI K I Km’

Inhibited Enzyme Kinetics Uncompetitive inhibitors (I)

Inhibited Enzyme Kinetics Uncompetitive inhibitors (I) we can obtain, - in Lineweaver- Burk Plot

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors - can cause inhibition at substrate concentration - bind only to the. Assume rapid equilibrium, E+S + S ES 2 K SI Km’

Substrate Inhibition

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors (I)

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors (I) we can obtain, At low substrate concentration<<1 At high substrate concentration Michaelis-Menten Equation

Inhibited Enzyme Kinetics Uncompetitive substrate inhibitors (I) The substrate concentration resulting in the maximum reaction rate can be determined by setting dv/d[S]=0, [S] max is given by

Uncompetitive substrate inhibitors (I) Determine [S] max:

Inhibition Estimation Product formation rate v ~ [S]: v has a peak? If yes, then it’s substrate inhibition. - get [S] max from the plot of v~[s]. - at low substrate concentration, obtain Vm and Km’ graphicallyor through direct calculation. - calculate K I through If no, then examine the data with and without inhibitors in 1/v ~ 1/[S] plot (Lineweaver-Burk Plot).

Estimation of Inhibited Enzyme Kinetics

Determine the type of inhibition. Determine the parameters for Michaelis- Menten equation without inhibition. Determine the parameter of KI for inhibited kinetics.

Summary of Inhibited Kinetics For reversible enzyme inhibition, there are - competitive - noncompetitive - uncompetitive - substrate inhibition Determine parameters for all these types of inhibition kinetics.