Introduction:

Metabolic pathways are tightly regulated through feedback inhibition to maintain balance in the production of essential metabolites. In certain cases, mutations can lead to the overproduction of a metabolite, disrupting the normal regulation. This article explores the likely mutation location that leads to the overproduction of metabolite ‘X’, which is feedback inhibited in the wild-type strain. Specifically, we’ll discuss a mutation in the gene coding for a homodimeric enzyme that catalyzes the first step in the biosynthesis of ‘X’.

Understanding the Feedback Inhibition Mechanism:

Feedback inhibition is a regulatory mechanism where the end product of a biosynthetic pathway inhibits an earlier step in the pathway. This prevents the unnecessary accumulation of metabolites. However, mutations in enzymes involved in this process can lead to the overproduction of the target metabolite, bypassing the inhibition.

In this case, the biosynthetic pathway of metabolite ‘X’ is feedback inhibited, and a mutation has caused overproduction of this metabolite. The mutation is likely affecting an enzyme involved in the initial step of the biosynthesis.

The Role of the Homodimeric Enzyme:

The enzyme in question is a homodimeric enzyme, meaning it is composed of two identical monomers that form a functional dimer. The enzyme catalyzes the first step in the biosynthetic pathway of metabolite ‘X’. For feedback inhibition to function properly, the end product typically binds to a regulatory site on the enzyme to prevent further enzyme activity. However, mutations in certain parts of the enzyme can disrupt this regulation, leading to overproduction.

Location of the Mutation:

Given that the enzyme is subject to feedback inhibition, a mutation that leads to overproduction of metabolite ‘X’ would most likely occur in regions of the enzyme that are involved in its regulatory control. Below are potential mutation locations:

1. The Catalytic Active Site: Mutations here could affect the enzyme’s ability to catalyze the reaction but are less likely to directly affect feedback inhibition. Such mutations would usually alter the efficiency of the enzyme but not its regulatory control.

2. The Regulatory Site: The most likely location for a mutation causing overproduction of ‘X’ would be in the regulatory site. Feedback inhibition occurs when the end product binds to this site and prevents enzyme activity. A mutation in the regulatory site could disrupt this feedback inhibition, allowing the enzyme to remain active even in the presence of high levels of the product. This would lead to the overproduction of metabolite ‘X’.

3. The Point of Contact Between the Two Monomers: The point of contact between the two monomers in a homodimeric enzyme could play a role in the enzyme’s overall structure and function. A mutation here could potentially alter enzyme activity, but it would be less likely to directly impact feedback inhibition unless it also affects the regulatory site.

4. In the Random Coil Structure of the Protein: The random coil structure typically refers to non-structured regions of a protein that are flexible and may not directly affect functional sites like the catalytic or regulatory sites. Mutations in these areas might alter the enzyme’s folding but are less likely to directly impact the regulation of feedback inhibition.

Conclusion:

The mutation responsible for the overproduction of metabolite ‘X’ is most likely to occur in the regulatory site of the homodimeric enzyme. This site controls feedback inhibition, and a mutation here would prevent the end product from binding and inhibiting enzyme activity, leading to overproduction of metabolite ‘X’.

Answer:

The correct answer is 2. the regulatory site.