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. Following exposure to hypoxia, activated in HeLa cells but not in cardiovascular cells. 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 (PubMed:25974097). Interacts with HIF1A (PubMed:25974097). Mainly cytoplasmic. Shuttles between the nucleus and cytoplasm (PubMed:19631610). Nuclear export requires functional XPO1. According to PubMed:11056053, widely expressed with highest levels in skeletal muscle and heart, moderate levels in pancreas, brain (dopaminergic neurons of adult and fetal substantia nigra) and kidney, and lower levels in lung and liver. According to PubMed:12351678 widely expressed with highest levels in brain, kidney and adrenal gland. Expressed in cardiac myocytes, aortic endothelial cells and coronary artery smooth muscle. According to PubMed:12788921; expressed in adult and fetal heart, brain, liver, lung, skeletal muscle and kidney. Also expressed in placenta. Highest levels in adult heart, brain, lung and liver and fetal brain, heart spleen and skeletal muscle. 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-323 or Cys-326. Variations in EGLN1 are associated with adaptation to high altitude (PubMed:20838600, PubMed:20466884, PubMed:24711448, PubMed:25129147). High-altitude hypoxia (reduced inspired oxygen tension due to decreased barometric pressure) exerts severe physiological stress on the human body and leads to an elevation of hematocrit levels and an increased number of erythrocytes (polycythemia) in non-adapted individuals. Genetic variations in EGLN1 contribute to adaptation to high altitute by maintaining hematocrit levels comparable to those for populations living at sea level and are present in two high-altitude regions where humans have lived for millennia, the Andean Altiplano and the Tibetan Plateau (PubMed:20838600, PubMed:20466884). Variants Glu-4 and Ser-127, which are frequently associated together and are present in the majority of Tibetan populations, participate in adaptation to high altitude (PubMed:24711448, PubMed:25129147). Molecular mechanisms explaining this adaptation are however unclear. According to a report, variants Glu-4 and Ser-127 lead to decreased interaction with PTGES3 and subsequent decrease of HIF alpha proteins degradation (PubMed:24711448). According to a second report, Glu-4 and Ser-127 haplotype enhances the catalytic activity under hypoxic conditions, promoting increased HIF alpha proteins degradation, thereby abrogating hypoxia-induced and HIF alpha-mediated augmentation of erythropoiesis and protecting Tibetans from polycythemia at high altitude (PubMed:25129147). The disease is caused by variants affecting the gene represented in this entry. Inactive isoform. It was previously reported that this protein was the ortholog of rat SM-20. However, EGLN3 is now considered the true ortholog of rat SM-20 since it shows substantially greater similarity. Truncated N-terminus.