Question

The inhibition of succinic dehydrogenase by malonate is an example
A. Competitive inhibition
B. Non-competitive inhibition
C. Allosteric inhibition
D. Enzyme repression

Answer 1

Succinic dehydrogenase is a respiratory enzyme, primarily functions in the Krebs cycle and the Electron Transport Chain. It is present in the inner mitochondrial membrane and is responsible for the conversion of Succinate to Fumarate in the Krebs cycle and derives electrons in the respiratory chain to reduce oxygen to form water and ATP.

Complete answer:
- Competitive inhibition: In this, the substrate and the inhibitor exhibit structural similarity due to which they compete for the same active site. Competitive inhibitors are also called structural analogs. They function by decreasing the proportion of enzymes available for substrate binding. It can be relieved by increasing substrate concentration because, at high substrate concentration, the competitive inhibitor will displace from the active site by Le Chatelier principle and ${V_{max}}$ can be attained. In competitive inhibition,${V_{max}}$remains the same as before but $K_M$ increases. eg. inhibition of succinic dehydrogenase by malonate.
- Non-competitive inhibition: In this, inhibitors bind to the allosteric site (regulatory site) of the enzyme and alters the three-dimensional structure of the active site so that the substrate can not fit into it. It either binds to the free enzyme or to the enzyme-substrate complex and the enzyme will remain inhibited until the non-competitive inhibitor leaves the regulatory site. In this, the $K_M$ remains the same, but the${V_{max}}$ decreases.
- Allosteric inhibition is also referred to as non-competitive inhibition.
- Enzyme repression: It is also known as feedback inhibition. In this, the final product of an enzyme-catalyzed reaction is the inhibitor for the same enzyme so as to keep the activity of the enzyme in check.

Therefore, the correct answer is (A) Competitive inhibition.

Note:
Inhibitions are classified on the basis of their reversibility. There are reversible inhibitions, which include Competitive, Non-competitive, Uncompetitive, and Mixed inhibition. Another is Irreversible inhibition which includes Group-specific and Suicide inhibition.