Question

The antimicrobial agent mercuric chloride functions by

• A. Interfering with cellular oxidation process.
• B. Inhibiting the enzymes which contain the sulfhydryl group.
• C. Alkylation reactions with organic compounds such as enzymes and other proteins.
• D. Denaturation of proteins, interference with glycolysis and membrane damage.

Hint:

Remember that heavy metals like mercury, silver, and arsenic are "sulfhydryl seekers." They poison cells by attacking the -SH groups in proteins, effectively shutting down vital enzymes.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Mercuric chloride (HgCl\(_2\)) is a heavy metal compound that acts as a potent antimicrobial agent. Heavy metals typically exert their toxic effects by binding to and inactivating key cellular proteins, particularly enzymes.
Step 2: Detailed Explanation:


The mode of action of heavy metal ions like mercury (Hg\(^{2+}\)) is primarily through their high affinity for sulfhydryl (-SH) groups found in the amino acid cysteine.

When Hg\(^{2+}\) binds to the sulfhydryl groups of a protein, it forms a stable mercaptide (Protein-S-Hg-S-Protein).

This binding disrupts the protein's tertiary structure and inactivates its active site, especially in enzymes where cysteine residues are often crucial for catalytic activity. This process is known as sulfhydryl group inhibition.

While general protein denaturation (Option D) can occur at high concentrations, the most specific and primary mechanism at biocidal concentrations is the targeted inhibition of sulfhydryl-containing enzymes.

Option C, alkylation, is a mechanism of other agents like ethylene oxide. Option A is too general.

Step 3: Final Answer:
The primary antimicrobial function of mercuric chloride is inhibiting enzymes by binding to their sulfhydryl groups.