Question

An example of non-competitive inhibition is
A. Inhibition of succinic acid by malonate
B. Cyanide action on cytochrome oxidase
C. Sulpha drug on folic acid synthesizing bacteria
D. Inhibition of hexokinase by glucose-6- phosphate

Answer 1

Hint:Enzymes are proteins which act as a biological catalyst. They help in the acceleration of the reaction. The enzymes act on substrates and convert them into products. Enzymes don’t rise to undesired levels they are kept in check by enzyme inhibition.

Complete answer:
Enzyme inhibition (reversible) is of two types- competitive inhibition and non-competitive inhibition.
- Competitive inhibition is when the inhibitor binds to the active site of the enzyme and thus prevents the attachment of the substrate. The value of Michaelis Menten constant increases in this type of inhibition.
- Non-competitive inhibition occurs when the inhibitor binds to sites other than the active site of the enzyme. It prevents the attachment of the substrate to the active site. The value of Michaelis Menten constant remains unchanged for such a type of reaction.
Type of reaction that takes place in each of the given option is discussed below:
- Inhibition of succinate acid by malonate is an example of competitive inhibition where malonate molecule binds to the active site because the spacing of its carboxyl groups is not greatly different from that of succinate. However, no catalytic reaction occurs because malonate does not have a CH2CH2 group to convert to CH=CH.
- Cyanide action on cytochrome oxidase is an example of non-competitive inhibition because cyanide acts as the inhibitor which attaches to cytochrome oxidase at a place other than the active site and brings a conformational change which in turn prevents the transport of electrons from cytochrome c to oxygen.
- Sulpha drug on folic acid synthesizing bacteria is an example of competitive inhibition. Sulpha drugs act as a competitive inhibitor by attaching to the active site of the enzyme. It then inhibits the growth and multiplication of bacteria by inhibiting the formation of folic acid.
- Inhibition of hexokinase by glucose-6-phosphate is an example of feedback inhibition. In feedback inhibition when an excess of product is formed the product changes its configuration to stop the action of the enzyme. In this case, glucose forms glucose-6-phosphate in the presence of enzyme hexokinase. When glucose-6-phosphate reaches an undesired level then it changes its configuration hence stopping the attachment of hexokinase.
So the correct answer is option B ‘cyanide action on cytochrome oxidase’.
Note:
- Enzyme inhibition is of two types- reversible and irreversible inhibition.
- When inhibitors attach to enzymes halting the process for some time only then it is called reversible inhibition. The inhibitors detach themselves when the product levels are decreased.
- When inhibitors attach to enzymes to permanently halt the enzyme activity then it is called irreversible inhibition.