Question

An example of non-competitive inhibition is-
A. The inhibition of succinic dehydrogenase by malonate
B. Cyanide action on cytochrome oxidase
C. Sulpha drugs on folic acid synthesizing bacteria
D. The inhibition of hexokinase by glucose-6-phosphate
E. Both B and D

Answer 1

Hint:- A kind of enzyme inhibition in which the inhibitor decreases the enzyme 's activity and binds equally well to the enzyme, whether or not the substrate has already been bound. It is distinct from general mixed inhibition in that the enzyme and the enzyme-substrate complex have an equal affinity for the inhibitor.

Complete step-by-step solution:-
Option A is incorrect. Malonate inhibition of succinate dehydrogenase is an instance of negative feedback. A classic example of competitive inhibition with succinic acid as its substrate is the enzyme succinate dehydrogenase. It is possible to quantitatively evaluate competitive inhibition by steady-state kinetics. Since the inhibitor binds to the enzyme reversibly, by simply adding more substrate, rivalry may be skewed in favour of the substrate.
Option B is correct. The inhibitor binds to the enzyme at a position other than the substrate binding site for non-competitive inhibition. It results in enzyme activity being destroyed. The substrate can combine with such an enzyme, but it is inhibited by product formation. Cyanide, for example, prevents the activity of cytochrome oxidase by irreversibly combining cytochrome oxidase with copper.
Option C is incorrect. Nucleic acid is synthesised using folic acid or folate. In the presence of the enzyme dihydropteroate synthase for folic acid synthesis in bacteria, dihydropteridine and p-aminobenzoic acid react. By binding to the enzyme's active site, sulpha drugs serve as a competitive inhibitor and thus inhibit the growth and replication of bacteria by inhibiting the production of folic acid.
Option D is incorrect. A regulatory enzyme that catalyses the entry of glucose into the glycolytic pathway is hexokinase. The conversion of glucose into glucose-6-phosphate is catalysed by the enzyme. Hexokinase is extremely glucose-affinized. Hexokinase is inhibited allosterically by its own substance, glucose-6-phosphate. As the glucose-6-phosphate concentration increases, it binds to the enzyme at its allosteric site and causes the enzyme to change conformationally. The enzyme can no longer bind to glucose because of this and the forward reaction is inhibited. This form of inhibition is known as the inhibition of feedback.
Option E is incorrect. An example of non-competitive inhibition is cyanide inhibiting cytochrome oxidase activity by irreversibly combining cytochrome oxidase with copper, while Hexokinase has a high affinity for glucose. An example of allosteric inhibition is that hexokinase is allosterically inhibited by its own product, which is glucose-6-phosphate.
So, the correct answer is Option B.

Note:- The primary distinction between competitive and non-competitive is that competitive inhibition affects the ability of the substrate to bind by binding an inhibitor instead of a substrate, thus reducing the substrate 's affinity to the enzyme. The inhibitor binds to an allosteric site in non-competitive inhibition and prevents a chemical reaction from being performed by the enzyme-substrate complex. This does not impact the enzyme's Km (affinity) (for the substrate).