Is involved in the final hydroxylation step of the post-translational modification of translation elongation factor P (EF-P) on 'Lys-34'. Acts after beta-lysylation of 'Lys-34' by EpmA and EpmB. EpmC adds an oxygen atom to the C5 position of 'Lys-34' and does not modify the added beta-lysine. Hydroxylation activity is abolished by NADP and increased by NADPH. EF-P proteins in the mutant strain displays a modification of +128 Da, whereas a modification of +144 Da is observed in wild-type strains. Cells lack CadA activity (lysine decarboxylase). Belongs to the EpmC family.