The graph below shows the activity of enzyme pepsin in the presence of inhibitors aliphatic alcohols (P) or N-acetyl-1-phenylalanine (Q). Which ONE of the following represents the nature of inhibition by P and Q, respectively? 
To determine the nature of inhibition represented by P and Q, we examine the Lineweaver-Burk plot shown in the graph. This plot is a double reciprocal graph of the Michaelis-Menten equation, where the y-axis represents \( \frac{1}{V_0} \) (the reciprocal of reaction velocity) and the x-axis represents \( \frac{1}{[S]} \) (the reciprocal of substrate concentration).
In enzyme kinetics, the type of inhibition can be inferred from the shifts seen in the graph:
- Competitive Inhibition: This type of inhibition occurs when the inhibitor competes with the substrate for binding to the active site of the enzyme. On a Lineweaver-Burk plot, competitive inhibition is indicated by lines intersecting on the y-axis. Since both the inhibitor and the substrate cannot bind simultaneously, the \( K_m \) value (x-intercept) changes, but the \( V_{max} \) (y-intercept) remains the same.
- Non-competitive Inhibition: In this type, the inhibitor binds to a site other than the active site and can bind simultaneously with the substrate. Non-competitive inhibition is shown by parallel lines on a Lineweaver-Burk plot, indicating that the \( V_{max} \) decreases while the \( K_m \) remains unchanged.
Based on the graph provided:
- Line P represents a scenario where the lines intersect at the y-axis, indicating a competitive inhibition.
- Line Q shows a parallel shift compared to the uninhibited line, indicating non-competitive inhibition.
Therefore, the nature of inhibition by P and Q is Competitive and Non-competitive, respectively.
Important Questions from Enzyme Kinetics Michaelis Menten K_m V_{max}
- An enzyme following Michaelis-Menten kinetics, catalyses a reaction with an initial velocity ($V_0$) of $2\ \mu\text{M s}^{-1}$ at the substrate concentration of $10\ \mu\text{M}$. If the turnover number ($k_{\text{cat}}$) of the enzyme for the given substrate is $500\ \text{s}^{-1}$ and the enzyme concentration in the reaction is $0.01\ \mu\text{M}$, then the value of the Michaelis-Menten constant ($K_m$) would be__________ $\times\ 10^{-6}\ \text{M}$ (in integer).
The following plot represents the Lineweaver-Burk equation of an enzymatic reaction both in the presence and the absence of inhibitor. Here, V is the velocity of reaction and S is the substrate concentration.
The nature of inhibition shown in the plot is
- For an enzyme catalyzed reaction, the plot that correctly represents the relationship between the rate and temperature is
- In an enzyme catalyzed reaction, the initial reaction velocity is only one fourth of its maximum velocity. If the substrate concentration is $3.0 \times 10^{-3}$ mM, the value of $K_m$ in micro molar ($\mu$M) will be ....
- The Lineweaver-Burk plot of an enzymatic reaction shows $V_{max}$ of $160 \, \mu mol/l.min$ and $k_m$ of $60 \, \mu mol/l$. For a substrate concentration of $40 \, \mu mol/l$, the velocity of the reaction is estimated to be __________ $\mu mol/l.min$.
