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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 two dimers are connected to each other via a coiled-coil motif. [[Image:PAH tetramer]] Each monomeric subunit is composed of three sites: the N-terminal, the catalytic site, and the C-terminal. <ref name= "flydal"/>. | Mammalian PAH is a homo-tetrameric enzyme of 50 kDa subunits composed of two asymmetric dimeric units. The two dimers are connected to each other via a coiled-coil motif. [[Image:PAH tetramer.jpg]] Each monomeric subunit is composed of three sites: the N-terminal, the catalytic site, and the C-terminal. <ref name= "flydal"/>. | ||
PAH enzyme has been studied extensively because of its correlation with the genetic defective condition phenylketonuria (PKU). Errors in the function or stability of PAH lead to its malfunction which causes a buildup of phenylalanine resulting in numerous health detriments. | PAH enzyme has been studied extensively because of its correlation with the genetic defective condition phenylketonuria (PKU). Errors in the function or stability of PAH lead to its malfunction which causes a buildup of phenylalanine resulting in numerous health detriments. | ||
