Prolyl 3-hydroxylase that catalyzes the post-translational formation of 3-hydroxyproline on collagens (PubMed:18487197). Contributes to proline 3-hydroxylation of collagen COL4A1 and COL1A1 in tendons, the eye sclera and in the eye lens capsule (By similarity). Has high activity with the type IV collagen COL4A1, and lower activity with COL1A1 (PubMed:18487197). Catalyzes hydroxylation of the first Pro in Gly-Pro-Hyp sequences where Hyp is 4-hydroxyproline (PubMed:18487197). Has no activity on substrates that lack 4-hydroxyproline in the third position (PubMed:18487197). 2-oxoglutarate + L-prolyl-[collagen] + O2 = CO2 + succinate + trans-3-hydroxy-L-prolyl-[collagen] Inhibited by pyridine 2,4-dicarboxylate, an analog of 2-oxoglutarate. Expression localized to the epithelia of bile ducts and to the sacroplasm of heart muscle and skeletal muscle. In the pancreas, localized to a subpopulation of Langerhans islet cells and in the salivary gland, expressed in acinar cells (at protein level) (PubMed:15063763). Expressed in adult heart, placenta, lung, liver, skeletal muscle and kidney (PubMed:15063763, PubMed:18487197). Detected in fetal heart, spleen, lung, liver skeletal muscle and kidney (PubMed:18487197). The disease is caused by variants affecting the gene represented in this entry. Belongs to the leprecan family. Truncated N-terminus.