Cellular oxygen sensor that catalyzes, under normoxic conditions, the post-translational formation of 4-hydroxyproline in hypoxia-inducible factor (HIF) alpha proteins. Hydroxylates a specific proline found in each of the oxygen-dependent degradation (ODD) domains (N-terminal, NODD, and C-terminal, CODD) of HIF1A. Also hydroxylates HIF2A. Has a preference for the CODD site for both HIF1A and HIF1B. Hydroxylated HIFs are then targeted for proteasomal degradation via the von Hippel-Lindau ubiquitination complex. Under hypoxic conditions, the hydroxylation reaction is attenuated allowing HIFs to escape degradation resulting in their translocation to the nucleus, heterodimerization with HIF1B, and increased expression of hypoxy-inducible genes. EGLN1 is the most important isozyme under normoxia and, through regulating the stability of HIF1, involved in various hypoxia-influenced processes such as angiogenesis in retinal and cardiac functionality. Target proteins are preferentially recognized via a LXXLAP motif. 2-oxoglutarate + L-prolyl-[hypoxia-inducible factor alpha subunit] + O2 = CO2 + succinate + trans-4-hydroxy-L-prolyl-[hypoxia-inducible factor alpha subunit] Binds 1 Fe(2+) ion per subunit. Monomer. Interacts with ING4; the interaction inhibits the hydroxylation of HIF alpha proteins. Interacts with PTGES3 (via PXLE motif); thereby recruiting EGLN1 to the HSP90 pathway to facilitate HIF alpha proteins hydroxylation. Interacts with LIMD1. Found in a complex composed of LIMD1, VHL, EGLN1/PHD2, ELOB and CUL2. Interacts with EPAS1. Interacts with CBFA2T3 and HIF1A. Mainly cytoplasmic. Shuttles between the nucleus and cytoplasm. Nuclear export requires functional XPO1. Expressed in heart, brain liver, skeletal muscle and kidney. Low levels were detected in the lung. Constitutively expressed during differentiation of C2C12 skeletal myocytes. Induced by growth factors in cultured vascular smooth muscle. Up-regulated in proliferating myoblasts induced to form differentiated myotubes. The beta(2)beta(3) 'finger-like' loop domain is important for substrate (HIFs' CODD/NODD) selectivity. S-nitrosylation inhibits the enzyme activity up to 60% under aerobic conditions. Chelation of Fe(2+) has no effect on the S-nitrosylation. It is uncertain whether nitrosylation occurs on Cys-300 or Cys-303. Null mice are smaller than wild type and are erythematous with some animals having evidence of retroperitoneal hemorrhage. The resulting polycythemia can cause thrombosis and cardiac failure and animals die off after 10 weeks. Erythropoietin levels are increased in kidneys but not in livers. In neonatal null mice exposed to 75% oxygen, there are high levels of HIF1A nuclear abundance in retinal tissues accompanied by well-preserved retinal microvessels compared to wild type where oxygen-treated retinas exhibit reverse effects with increased risks of retinopathy. Truncated N-terminus.