Selenocysteine is often found in the active sites of enzymes that catalyze redox reactions due to its unique chemical properties. The selenol group (-SeH) in selenocysteine is more nucleophilic and has a lower pKa compared to the thiol group (-SH) in cysteine, making it a superior catalytic agent in oxidation-reduction reactions. This property is particularly important in antioxidant defense mechanisms, where selenoproteins like glutathione peroxidases and thioredoxin reductases play critical roles.
