Enzyme kinetics & Michaelis-Menten Equation Abdul Rehman Abbasi MSc Chemistry Semester – I Preston University Isb.

Michaelis-Menten kinetics EQUATION STEADY STATE GRAPH

 ENZYME KINETICS is the study of the chemical reactions that are catalyzed by enzymes.  In Enzyme Kinetics, The Reaction rate is measured and the effect of varying the condition of the reaction is investigated.  Studying an enzyme’s kinetics in this way we can reveal the catalytic mechanism of this enzyme. Enzyme Kinetics

 Michaelis-Menten Kinetics is one of the simplest and best know models of enzyme kinetics.  The model serves to explain how an enzyme can cause kinetic rate enhancement of a reaction and why the rate of reaction depends on the concentration of enzymes present. Michaelis-Menten Analysis

Enzyme Kinetics Equation

Here,  E = Enzymes  S = Substrate  ES = Enzyme-Substrate Complex  P = Product  K = Rate of reaction

Steady State Assumptions  To understand Michaelis- Menten kinetics, we’ll use the general enzyme reaction scheme including both backward and forward reaction i.e. E + S ↔ k−1 k1 ES → k-2 k2 E + P  The ES complex is formed by combining Enzyme E with Substrate S at rate constant k1. The ES can either dissociate to form E f (Free Enzyme) and P (Product) at rate constant k2 and k3.

Steady State Assumption  E + S ↔ k −1 k1 ES → k2 E + P  Steady State Assumption [ES] Constant  Formation of ES = Loss of ES  Rate 1 + Rate 2 = Rate -1 + Rate -2  Here Rate -2 is very Small so we will just neglect its value and we’ll get  E + S ↔ k −1 k1 ES → k2 E + P

K M & V max  K m Known as Michaelis-Menten Constant  Defined as the substrate concentration at 1/2 the maximum velocity.  V max represents the maximum velocity achieved by the system, at maximum (saturating) substrate concentrations.

Significance of K m and V max  K m is [S] at ½ V max  It is constant for a given enzyme at particular temp and pressure.  Small K m = Tight Bonding.  Large K m = Weak Bonding.  It is the measure of substrate concentration required for an effective catalysis.

Significance of K m and V max  V max is theoretical maximal velocity  Vmax is constant for a given enzyme.  To reach v max, All enzymes molecules have to be bounded by substrate.  K cat is a measure of catalytic activity  Catalytic Efficiency = K cat / K m  Allows comparison of effectiveness of an enzyme for different substrates.