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'''Phenylalanine Hydroxylase''' (also known as Phenylalanine-4-monooxygenase or simply PAH) is the enzyme that catalyzes the conversion of L-phenylalanine into L-tyrosine by hydroxylation (addition of an -OH group) of the aromatic side chain of phenyalanine. This reaction is the initial and rate-limiting step in the phenylalanine catabolism pathway. The tyrosine product (a non-essential amino acid) can then serve as a precursor to the synthesis of important neurotransmitters.<ref name= "flydal"> Flydal, Marte, and Aurora Martinez. "Phenylalanine Hydroxylase: Function, Structure, and Regulation." International Union of Biochemistry and Molecular Biology Journal 65.4 (2013): 341-349. Web. </ref>. PAH uses tetrahydrobiopterin (BH4)as a cofactor and has a nonheme iron atom bound to its active site. PAH is classified as an oxidoreductase, specifically enzyme class EC 1.14 since its mechanism of action involves the oxidation/reduction of its substrate. <ref name= "pdb"> http://www.rcsb.org/pdb/explore/explore.do?structureId=1J8U </ref>. | '''Phenylalanine Hydroxylase''' (also known as Phenylalanine-4-monooxygenase or simply PAH) is the enzyme that catalyzes the conversion of L-phenylalanine into L-tyrosine by hydroxylation (addition of an -OH group) of the aromatic side chain of phenyalanine. This reaction is the initial and rate-limiting step in the phenylalanine catabolism pathway. The tyrosine product (a non-essential amino acid) can then serve as a precursor to the synthesis of important neurotransmitters.<ref name= "flydal"> Flydal, Marte, and Aurora Martinez. "Phenylalanine Hydroxylase: Function, Structure, and Regulation." International Union of Biochemistry and Molecular Biology Journal 65.4 (2013): 341-349. Web. </ref>. PAH uses tetrahydrobiopterin (BH4)as a cofactor and has a nonheme iron atom bound to its active site. PAH is classified as an oxidoreductase, specifically enzyme class EC 1.14 since its mechanism of action involves the oxidation/reduction of its substrate. <ref name= "pdb"> http://www.rcsb.org/pdb/explore/explore.do?structureId=1J8U </ref>. | ||
PAH enzyme is present in the liver cells of humans and other mammals. It is also present in non-mammalian eukaryote organisms and some bacteria such as ''E.coli''. <ref name= "pdb"/>. Recently, it has been identified in some protozoans and slime molds, and even in nonflowering plants such as spinach from which it has been extracted and studied. <ref> Nair, P, and L Vining. "Phenylalanine Hydroxylase from Spinach Leaves." Phytochemistry 4.3 (1965): 401-411. Web. </ref>. | PAH enzyme is present in the liver cells of humans and other mammals. It is also present in non-mammalian eukaryote organisms and some bacteria such as ''E.coli''. <ref name= "pdb"/>. Recently, it has been identified in some protozoans and slime molds, and even in nonflowering plants such as spinach from which it has been extracted and studied. <ref> Nair, P, and L Vining. "Phenylalanine Hydroxylase from Spinach Leaves." Phytochemistry 4.3 (1965): 401-411. Web. </ref>. | ||
Mammalian PAH is a homo-tetrameric enzyme of 50 kDa subunits composed of two asymmetric dimeric units. The | Mammalian PAH is a homo-tetrameric enzyme of 50 kDa subunits composed of two asymmetric dimeric units. The four subunits are connected to each other via a coiled-coil motif as shown in the diagram below. | ||
[[Image:PAH tetramer complex.jpg]] | [[Image:PAH tetramer complex.jpg]] | ||
