procollagen-proline 4-dioxygenase complex cellular_component prolyl 4-hydroxylase complex GO:0016222 procollagen-proline, 2-oxoglutarate-4-dioxygenase complex A protein complex that catalyzes the formation of procollagen trans-4-hydroxy-L-proline and succinate from procollagen L-proline and 2-oxoglutarate, requiring Fe2+ and ascorbate. Contains two alpha subunits that contribute to most parts of the catalytic sites, and two beta subunits that are identical to protein-disulfide isomerase. endoplasmic reticulum protein-containing complex oxidoreductase complex