Arginine hydroxylase involved in the assembly of mitochondrial NADH:ubiquinone oxidoreductase complex (complex I, MT-ND1) at early stages (PubMed:18940309, PubMed:27226634). Acts by mediating hydroxylation of 'Arg-111' of NDUFS7 (PubMed:27226634). May also have methyltransferase activity (Probable). Interacts with NDUFAF8, leading to stabilize NDUFAF5 (PubMed:27499296). Interacts with NDUFS7 (PubMed:27226634). Peripherally localized on the matrix face of the mitochondrial inner membrane. The disease is caused by variants affecting the gene represented in this entry. Belongs to the methyltransferase superfamily.