Enzyme Inhibition Analysis

The question asks about the effect of malonate on succinate dehydrogenase activity.

Mechanism of Inhibition

Malonate is structurally similar to the substrate, succinate. This structural similarity allows malonate to bind to the active site of succinate dehydrogenase, acting as a competitive inhibitor.

Kinetic Effects of Competitive Inhibition

Competitive inhibitors compete with the substrate for the enzyme's active site. This competition affects the enzyme kinetics as follows:

• The apparent Michaelis constant ($K_m^{app}$) increases because a higher substrate concentration is needed to achieve half-maximal velocity ($V_{max}/2$) in the presence of the inhibitor. The relationship is given by $K_m^{app} = K_m \times (1 + \frac{[I]}{K_i})$, where $[I]$ is the inhibitor concentration and $K_i$ is the inhibition constant.
• The maximum velocity ($V_{max}$) remains unchanged, as the inhibition can be overcome by sufficiently high substrate concentrations, ensuring the enzyme eventually reaches its maximum catalytic rate.

Graphical Representation (Michaelis-Menten Plot)

A Michaelis-Menten plot graphs reaction velocity ($v$) against substrate concentration ([S]). In the case of competitive inhibition:

• The curve representing the reaction with the inhibitor is shifted to the right compared to the uninhibited reaction curve.
• Both curves eventually plateau at the same $V_{max}$.

The graph representing this behavior is shown in Option 1.

In this graph, the inhibited reaction (lower curve) requires higher substrate concentrations to reach a given velocity compared to the uninhibited reaction (upper curve), but both reactions reach the same maximum velocity ($V_{max}$). This is consistent with competitive inhibition by malonate.