The function of NDUFAF5 (NADH:ubiquinone oxidoreductase complex assembly factor 5, ENSG00000101247) is as follows. Arginine hydroxylase that mediates hydroxylation of 'Arg-111' of NDUFS7 and is involved in the assembly of mitochondrial NADH:ubiquinone oxidoreductase complex (complex I, MT-ND1) at early stages (PubMed:18940309, PubMed:27226634). May also have methyltransferase activity (Probable). {ECO:0000269|PubMed:18940309, ECO:0000269|PubMed:27226634, ECO:0000305}.