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. [ http://www.ncbi.nlm.nih.gov/pubmed/14500733 http://www.ncbi.nlm.nih.gov/pubmed/7753822 ]