Zinc is an essential trace element for most organisms and is present in the active site of the enzyme carboxypeptidase. Zinc likely functions as a Lewis acid, which means that it can accept a pair of electrons from a substrate molecule. This allows the enzyme to catalyze the hydrolysis of peptide bonds in proteins, releasing the C-terminal amino acid. Zinc is also important for the structural stability of carboxypeptidase and helps to maintain the enzyme's active conformation.