Catalyzes the conversion of prostaglandin H2 (PGH2) to thromboxane A2 (TXA2), a potent inducer of blood vessel constriction and platelet aggregation (PubMed:8436233, PubMed:11297515, PubMed:9873013, PubMed:11097184, PubMed:24009185, PubMed:22735388). Cleaves also PGH2 to 12-hydroxy-heptadecatrienoicacid (12-HHT) and malondialdehyde, which is known to act as a mediator of DNA damage. 12-HHT and malondialdehyde are formed stoichiometrically in the same amounts as TXA2 (PubMed:11297515, PubMed:9873013, PubMed:22735388). Additionally, displays dehydratase activity, toward (15S)-hydroperoxy-(5Z,8Z,11Z,13E)-eicosatetraenoate (15(S)-HPETE) producing 15-KETE and 15-HETE (PubMed:17459323). prostaglandin H2 = thromboxane A2 prostaglandin H2 = (12S)-hydroxy-(5Z,8E,10E)-heptadecatrienoate + malonaldehyde a hydroperoxyeicosatetraenoate = an oxoeicosatetraenoate + H2O (15S)-hydroperoxy-(5Z,8Z,11Z,13E)-eicosatetraenoate = 15-oxo-(5Z,8Z,11Z,13E)-eicosatetraenoate + H2O (15S)-hydroperoxy-(5Z,8Z,11Z,13E)-eicosatetraenoate + AH2 = (5Z,8Z,11Z,13E,15S)-hydroxyeicosatetraenoate + A + H2O Lipid metabolism; fatty acid metabolism. Monomer. Platelets, lung, kidney, spleen, macrophages and lung fibroblasts. The disease is caused by variants affecting the gene represented in this entry. Thromboxane synthetase deficiency has been detected in some patients with a bleeding disorder due to platelet dysfunction. Belongs to the cytochrome P450 family. It is uncertain whether Met-1 is the initiator. An alternative upstream Met is found in primates, but not in other mammals. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. Extended N-terminus. CYP5A1 alleles