Which trace element tends to bind sulfhydryl groups in proteins?

• A. Cadmium
• B. Lead
• C. Thallium
• D. Mercury

Answer: (A)

Sulfhydryl groups (-SH) on cysteine residues are highly reactive and essential for the activity of many proteins. When a metal ion binds to these thiol groups, it blocks the reactive sulfur, disrupts disulfide-bond dynamics, and can cause conformational changes that inactivate the protein. Cadmium forms stable Cd–S interactions with these thiol sites, effectively inactivating sulfhydryl-dependent enzymes and disrupting protein structure. This tendency to bind SH groups explains many of cadmium’s toxic effects in tissues. While other metals like mercury can also target thiols, the scenario described emphasizes cadmium’s strong affinity for sulfhydryl groups in proteins.