L-prolyl-[hypoxia-inducible factor alpha subunit] + 2-oxoglutarate + O2 <=> trans-4-hydroxy-L-prolyl-[hypoxia-inducible factor alpha subunit] + succinate + CO2
l-prolyl-[hypoxia-inducible factor alpha subunit] + 2-oxoglutarate + o2 <=> trans-4-hydroxy-l-prolyl-[hypoxia-inducible factor alpha subunit] + succinate + co2