In molecular biology the DHHC domain is a protein domain that acts as an enzyme, which adds a palmitoyl chemical group to proteins in order to anchor them to cell membranes. The DHHC domain was discovered in 1999 and named after a conserved sequence motif found in its protein sequence. Roth and colleagues showed that the yeast Akr1p protein could palmitoylate Yck2p in vitro and inferred that the DHHC domain defined a large family of palmitoyltransferases. In mammals twenty three members of this family have been identified and their substrate specificities investigated. Some members of the family such as ZDHHC3 and ZDHHC7 enhance palmitoylation of proteins such as PSD-95, SNAP-25, GAP43, Gαs. Others such as ZDHHC9 showed specificity only toward the H-Ras protein. However, a recent study questions the involvement of classical enzyme-substrate recognition and specificity in the palmitoylation reaction. Several members of the family have been implicated in human diseases.