Arginine hydroxylase involved in the assembly of mitochondrial NADH:ubiquinone oxidoreductase complex (complex I, MT-ND1) at early stages. Acts by mediating hydroxylation of 'Arg-111' of NDUFS7. May also have methyltransferase activity. Interacts with NDUFAF8, leading to stabilize NDUFAF5. Interacts with NDUFS7. Peripherally localized on the matrix face of the mitochondrial inner membrane. Belongs to the methyltransferase superfamily.