Heavy metal ions such as mercury and silver inhibit many enzymes irreversibly because they
- A. compete with the substrate for the active site
- B. raise the pH of the solution
- C. supply the enzyme with excess energy
- D. bind to the sulphydryl groups of the protein and destroy its shape
Explanation
These ions attack the sulphur containing side chains, breaking disulphide bridges and permanently distorting the tertiary structure, so the damage cannot be reversed by removing the inhibitor or adding more substrate. This is essentially poisoning rather than regulation, and it is why mercury contamination is so dangerous. A competitive inhibitor, by contrast, binds reversibly at the active site.
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