Final answer:
Biotin-dependent enzymes require magnesium (Mg²⁺) as a cofactor for their carboxylation reactions. Magnesium ions help decrease the overall negative charge during these reactions. Zinc and iron serve as cofactors for other enzymes, but magnesium is specific to biotin-dependent enzymes.
Step-by-step explanation:
The metal ion required by biotin-dependent enzymes is magnesium (Mg²⁺). These enzymes are key players in carboxylation reactions, where they use biotin to catalyze the transfer of a carboxyl group from activated carbonate to a substrate. Magnesium ions play a crucial role by reducing the overall negative charge during the catalysis, making the reaction more efficient. A typical carboxylation reaction involves the generation of carboxybiotin from the action of biotin on activated carbonate, with subsequent transfer of the carboxyl group to the substrate. This biochemical process is essential for various metabolic pathways.
Other metal ions also act as cofactors for different enzymes, stabilizing their structure and enhancing their function. For instance, zinc (Zn²⁺) is necessary for DNA polymerase, whereas iron (Fe²⁺) is a cofactor in some oxygen-transport and antioxidant enzymes. However, when considering the activity of biotin-dependent carboxylases, magnesium is the specific metal ion they require.