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. Increased activation in hypoxia. Hydroxylation of the C-terminal ODD domain (CODD) proline of HIF1A is activated by cyclosporin A (CsA). 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, liver, kidney, brain, liver and testis. Highest levels in heart, lowest in liver. Up-regulated by hypoxia especially in liver and testis. Levels up-regulated also in myocardial infarction predominantly in cardiomyocytes. 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-238 or Cys-241.