Question

In Michaelis-Menten equation, $K_{+1}$ stands for ________.}

• A. Dissolution constant
• B. Forward reaction rate constant
• C. Backward reaction rate constant
• D. Enzyme inhibition

Hint:

In chemical kinetics: - Plus sign in the subscript ($k_{+1}$, $k_{+2}$) $\rightarrow$ Forward steps.
- Minus sign in the subscript ($k_{-1}$) $\rightarrow$ Backward or reverse steps.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Michaelis-Menten model describes the kinetics of enzyme-catalyzed reactions.
The model assumes that the enzyme ($E$) and substrate ($S$) reversibly bind to form an intermediate enzyme-substrate complex ($ES$), which then breaks down to release the product ($P$) and regenerate the free enzyme ($E$).
Key Formula or Approach:
The chemical reaction sequence is represented as:
\[ E + S \underset{k_{-1}}{\overset{k_{+1}}{\rightleftharpoons}} ES \xrightarrow{k_{+2}} E + P \] where:
- $k_{+1}$ (or $K_{+1}$) is the rate constant for the forward association reaction.
- $k_{-1}$ (or $K_{-1}$) is the rate constant for the backward dissociation reaction.
- $k_{+2}$ (or $K_{+2}$, also called $k_{\text{cat}}$) is the rate constant for the conversion of complex to product.

Step 2: Detailed Explanation:
The rate constant $K_{+1}$ governs the rate of the forward step where free enzyme and free substrate collide and bind to form the $ES$ complex.
Because it represents the rate of the forward binding step in the first equilibrium phase of the reaction, it is defined as the Forward reaction rate constant (or association rate constant).
Other constants represent:
- $K_{-1}$ (C): Backward reaction rate constant.
- $K_m$ (Michaelis constant): Ratio of the rate of complex breakdown to its formation, calculated as $K_m = \frac{k_{-1} + k_{+2}}{k_{+1}}$.

Step 3: Final Answer:
In the Michaelis-Menten kinetic scheme, $K_{+1}$ stands for the forward reaction rate constant.