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ALOX12
ALOX12 (EC 1.13.11.31), also known as arachidonate 12-lipoxygenase, 12-lipoxygenase, 12S-Lipoxygenase, 12-LOX, and 12S-LOX is a lipoxygenase-type enzyme that in humans is encoded by the ALOX12 gene which is located along with other lipoyxgenases on chromosome 17p13.3. ALOX12 is 75 kilodalton protein composed of 663 amino acids.
Other systematic names for ALOX12 include 12S-Lipoxygenase, platelet-type 12-lipoxygenase, arachidonate:oxygen 12-oxidoreductase, Delta12-lipoxygenase, 12Delta-lipoxygenase, and C-12 lipoxygenase. ALOX12, often termed plate platelet-type 12-lipoxygenase, is distinguished from leukocyte-type 12-lipoxygenase which is found in mice, rats, cows, and pigs but not humans. Leukocyte-type 12-lipoxygenase in these animal species shares 73-86% amino acid identity with human ALOX15 but only 57-66% identity with human platelet-type 12-lipoxygenase and, like ALOX15, metabolizes arachidonic acid primarily to 15(S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (i.e. 15(S)-HpETE; see 15-Hydroxyeicosatetraenoic acid). Accordingly, rodent leukocyte 12-lipoxygenase is deemed an ortholog of ALOX15 and is designated as Alox15.
Human ALOX12 and ALOX15 along with rodent leukocyte-type Alox12 and Alox15 are commonly termed 12/15-lipoxygenases based on their ability to metabolize arachidonic acid to both 12(S)-HpETE and 15(S)-HpETE and to conduct this same metabolism on arachidonic acid that is esterified to membrane phospholipids; human ALOX15B makes 15(S)-HpETE but not 12(S)-HpETE and therefore is not regarded as a 12/15-lipoxygenase. Studies on the role of ALOX12 in pathophysiology using the main models for such functional studies, rats and mice, are complicated because neither species possesses a lipoxygenase that makes a predominance of 12(S)-HETE and therefore is metabolically equivalent to ALOX12. For example, the functions inferred for Alox12 in mice made deficient in Alox12 using knockout methods may not indicate a similar function for ALOX12 in humans due to differences in these two enzymes' metabolic activities. The function of ALOX12 is further clouded by human ALOX15 which metabolizes arachidonic acid primarily to 15(S)-HpETE but also makes lesser but still significant amounts of 12(S)-HpETE (see ALOX15).
ALOX12 is also distinguished from arachidonate 12-lipoxygenase, 12R type (ALOX12B), which metabolizes arachidonic acid to the R stereoisomer of 12(S)-HpETE viz., 12(R)-hydroperoxy-5Z,8Z,10E,14Z-icosatetraenoic acid (12(R)-HpETE), a product with very different pathophysiological roles than that of 12(S)-HpETE (see ALOX12B).
ALOX12, originally called arachidonate 12-lipoxygenase, was first characterized by the Nobel Laureate, Bengt I. Samuelsson, and his famed colleague, Mats Hamberg, in 1974 by showing that human platelets metabolize arachidonic acid not only by the well-known cyclooxygenase pathway into prostaglandins and 12-hydroxyheptadecatrienoic acid but also by a cyclooxygenase-independent pathway to 12(S)-hydroperoxy-5,8,10,14-eicosatetraenoic acid; this activity was the first mammalian lipoxygenase activity to be characterized. In 1975, the first biological activity was attached to this metabolite in studies showing that it simulated the chemotaxis of human neutrophils. During the several years thereafter, human ALOX12 was purified, characterized biochemically, and had its gene molecularly cloned.
Based predominantly on the presence of its mRNA, human ALOX12 is distributed predominantly in blood platelets and leukocytes and at lower levels in the basal layer of the epidermis (particularly in the skin lesions of psoriasis), islets of Langerhans within the pancreas, and certain cancers.
The control of ALOX12 activity appears to rest principally on the availability of its polyunsaturated fatty acid (PUFA) substrates which are released from storage in membrane phospholipids by cell stimulation. The enzyme participates in arachidonic acid metabolism by conducting the following chemical reaction wherein its substrates are arachidonic acid (also termed as arachidonate or, chemically, as 5Z,8Z,11Z,14Z-eicosatetraenoic acid) and O2 (i.e. oxygen) and its product is 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (i.e. 12S-hydroperoxyeicosatetraenoic acid or 12S-HpETE):
In cells, 12SHpETE may be further metabolized by ALOX12 itself, by ALOXE3 or possibly other, as yet not fully identified, hepoxilin syntheses to hepoxilin A3 (8R/S-hydroxy-11,12-oxido-5Z,9E,14Z-eicosatrienoic acid) and B3 (10R/S-hydroxy-11,12-oxido-5Z,8Z,14Z-eicosatrienoic acid):
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ALOX12
ALOX12 (EC 1.13.11.31), also known as arachidonate 12-lipoxygenase, 12-lipoxygenase, 12S-Lipoxygenase, 12-LOX, and 12S-LOX is a lipoxygenase-type enzyme that in humans is encoded by the ALOX12 gene which is located along with other lipoyxgenases on chromosome 17p13.3. ALOX12 is 75 kilodalton protein composed of 663 amino acids.
Other systematic names for ALOX12 include 12S-Lipoxygenase, platelet-type 12-lipoxygenase, arachidonate:oxygen 12-oxidoreductase, Delta12-lipoxygenase, 12Delta-lipoxygenase, and C-12 lipoxygenase. ALOX12, often termed plate platelet-type 12-lipoxygenase, is distinguished from leukocyte-type 12-lipoxygenase which is found in mice, rats, cows, and pigs but not humans. Leukocyte-type 12-lipoxygenase in these animal species shares 73-86% amino acid identity with human ALOX15 but only 57-66% identity with human platelet-type 12-lipoxygenase and, like ALOX15, metabolizes arachidonic acid primarily to 15(S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (i.e. 15(S)-HpETE; see 15-Hydroxyeicosatetraenoic acid). Accordingly, rodent leukocyte 12-lipoxygenase is deemed an ortholog of ALOX15 and is designated as Alox15.
Human ALOX12 and ALOX15 along with rodent leukocyte-type Alox12 and Alox15 are commonly termed 12/15-lipoxygenases based on their ability to metabolize arachidonic acid to both 12(S)-HpETE and 15(S)-HpETE and to conduct this same metabolism on arachidonic acid that is esterified to membrane phospholipids; human ALOX15B makes 15(S)-HpETE but not 12(S)-HpETE and therefore is not regarded as a 12/15-lipoxygenase. Studies on the role of ALOX12 in pathophysiology using the main models for such functional studies, rats and mice, are complicated because neither species possesses a lipoxygenase that makes a predominance of 12(S)-HETE and therefore is metabolically equivalent to ALOX12. For example, the functions inferred for Alox12 in mice made deficient in Alox12 using knockout methods may not indicate a similar function for ALOX12 in humans due to differences in these two enzymes' metabolic activities. The function of ALOX12 is further clouded by human ALOX15 which metabolizes arachidonic acid primarily to 15(S)-HpETE but also makes lesser but still significant amounts of 12(S)-HpETE (see ALOX15).
ALOX12 is also distinguished from arachidonate 12-lipoxygenase, 12R type (ALOX12B), which metabolizes arachidonic acid to the R stereoisomer of 12(S)-HpETE viz., 12(R)-hydroperoxy-5Z,8Z,10E,14Z-icosatetraenoic acid (12(R)-HpETE), a product with very different pathophysiological roles than that of 12(S)-HpETE (see ALOX12B).
ALOX12, originally called arachidonate 12-lipoxygenase, was first characterized by the Nobel Laureate, Bengt I. Samuelsson, and his famed colleague, Mats Hamberg, in 1974 by showing that human platelets metabolize arachidonic acid not only by the well-known cyclooxygenase pathway into prostaglandins and 12-hydroxyheptadecatrienoic acid but also by a cyclooxygenase-independent pathway to 12(S)-hydroperoxy-5,8,10,14-eicosatetraenoic acid; this activity was the first mammalian lipoxygenase activity to be characterized. In 1975, the first biological activity was attached to this metabolite in studies showing that it simulated the chemotaxis of human neutrophils. During the several years thereafter, human ALOX12 was purified, characterized biochemically, and had its gene molecularly cloned.
Based predominantly on the presence of its mRNA, human ALOX12 is distributed predominantly in blood platelets and leukocytes and at lower levels in the basal layer of the epidermis (particularly in the skin lesions of psoriasis), islets of Langerhans within the pancreas, and certain cancers.
The control of ALOX12 activity appears to rest principally on the availability of its polyunsaturated fatty acid (PUFA) substrates which are released from storage in membrane phospholipids by cell stimulation. The enzyme participates in arachidonic acid metabolism by conducting the following chemical reaction wherein its substrates are arachidonic acid (also termed as arachidonate or, chemically, as 5Z,8Z,11Z,14Z-eicosatetraenoic acid) and O2 (i.e. oxygen) and its product is 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (i.e. 12S-hydroperoxyeicosatetraenoic acid or 12S-HpETE):
In cells, 12SHpETE may be further metabolized by ALOX12 itself, by ALOXE3 or possibly other, as yet not fully identified, hepoxilin syntheses to hepoxilin A3 (8R/S-hydroxy-11,12-oxido-5Z,9E,14Z-eicosatrienoic acid) and B3 (10R/S-hydroxy-11,12-oxido-5Z,8Z,14Z-eicosatrienoic acid):