Cytosolic deoxyhypusine hydroxylase (DOHH) complexed with Fe2+ catalyzes the irreversible hydroxylation of peptidyl deoxyhypusine (Dhp-K50-EIF5A) to peptidyl hypusine (Hyp-K50-EIF5A) using molecular oxygen. The only known substrate for this enzyme is the modified lysine at residue 50 of the two isoforms of eIF5A (Clement et al. 2003; Kang et al. 2007; Kim et al. 2006).