Question

Inhibition of Succinic dehydrogonase enzyme by malonate is a classical example of:

• A. Cofactor inhibition
• B. Feedback inhibition
• C. Competitive inhibition
• D. Enzyme activation

Answer 1

The Correct Option is C

Step 1: Enzyme Inhibition Defined

Enzyme inhibition occurs when a substance, termed an inhibitor, attaches to an enzyme, thereby diminishing its catalytic function. The nature of this interaction classifies inhibition as competitive, non-competitive, or uncompetitive.

Step 2: Competitive Inhibition Detailed

Competitive inhibition is characterized by an inhibitor molecule that structurally mimics the enzyme's substrate. Both compete for the enzyme's active site. When the inhibitor occupies the active site, it prevents substrate binding and reduces enzyme activity. Elevated substrate concentrations can, however, outcompete the inhibitor, mitigating its effect.

Step 3: Evaluation of Provided Options

Option 1: Non-competitive inhibition

In non-competitive inhibition, the inhibitor binds at a location distinct from the active site, inducing a conformational change that reduces enzyme efficacy. This mechanism is not operative with malonate and succinic dehydrogenase.

Option 2: Uncompetitive inhibition

Uncompetitive inhibition occurs when an inhibitor exclusively binds to the enzyme-substrate complex, thereby blocking the reaction's progression. This is not observed with malonate.

Option 3: Competitive inhibition

In this scenario, malonate contends with the natural substrate, succinate, for the active site of the enzyme succinic dehydrogenase. Malonate's structural similarity to succinate facilitates direct competition for binding, exemplifying competitive inhibition.

Option 4: Allosteric inhibition

Allosteric inhibition involves inhibitor binding to a site separate from the active site (an allosteric site), causing a conformational alteration that impacts enzyme activity. This is not pertinent to the interaction between malonate and succinic dehydrogenase.

Step 4: Conclusion Drawn

The observed interaction between malonate and succinic dehydrogenase represents competitive inhibition, as malonate directly competes with succinate for the enzyme's active site.

Answer: The correct identification is Option 3: Competitive inhibition.