Plays a key role in early steps of protein N-linked glycosylation by being required for the conversion of polyprenol into dolichol (PubMed:20637498). Dolichols are required for the synthesis of dolichol-linked monosaccharides and the oligosaccharide precursor used for N-glycosylation (PubMed:20637498). Acts as a polyprenol reductase that promotes the reduction of the alpha-isoprene unit of polyprenols into dolichols in a NADP-dependent mechanism (PubMed:20637498). Also able to convert testosterone (T) into 5-alpha-dihydrotestosterone (DHT) (PubMed:17986282, PubMed:26855069).
