Catalyzes the NAD-dependent oxidative cleavage of spermidine and the subsequent transfer of the butylamine moiety of spermidine to the epsilon-amino group of a critical lysine residue of the eIF-5A precursor protein to form the intermediate deoxyhypusine residue (PubMed:30661771). This is the first step of the post-translational modification of that lysine into an unusual amino acid residue named hypusine. Hypusination is unique to mature eIF-5A factor and is essential for its function.
Deoxyhypusine synthase (DHPS) utilizes spermidine and NAD as cofactors to incorporate a hypusine modification into the eukaryotic translation initiation factor 5A (eIF5A). Hypusine is essential for eIF5A activation, which, in turn, plays a key role in regulating protein translation of selected mRNA that are associated with the synthesis of oncoproteins, thereby enhancing tumor cell proliferation.