HDACs function as catalysts by facilitating the hydrolysis of acetyl groups from histone proteins. This enzymatic activity involves a nucleophilic attack on the carbonyl carbon of the acetyl group, resulting in the formation of a tetrahedral intermediate. The intermediate then collapses, releasing the acetyl group as acetate and restoring the lysine residue to its unacetylated state. This catalytic mechanism is highly efficient and tightly regulated within the cell.