Human Deoxyhypusine Synthase (DHS) is vital for the first step of hypusine biosynthesis. DHS catalyzes the NAD-dependent oxidative cleavage of spermidine, the subsequent transfer of the butylamine moiety of spermidine to the epsilon-amino group of a specific lysine residue of the eIF-5A precursor protein to form the intermediate deoxyhypusine residue.