title: Recombinant human phenylalanine hydroxylase is a substrate for the ubiquitin-conjugating enzyme system.
abstract: Mammalian phenylalanine hydroxylase (PAH) catalyses the conversion of L-phenylalanine to L-tyrosine in the presence of dioxygen and tetrahydrobiopterin; it is a highly regulated enzyme. Little is known about the rates of synthesis and degradation of PAH in vivo. The enzyme has been reported to have a half-life of approx. 2 days in rat liver and 7-8 h in rat hepatoma cells, but the mechanism of its degradation is not known. In the present study it is shown that the tetrameric form of the recombinant wild-type human enzyme is a substrate for the ubiquitin-conjugating enzyme system in the cytosolic fraction of rat testis. Our findings support the conclusion that multi-/poly-ubiquitination of human PAH plays a key role in the turnover of this cytosolic liver enzyme and provides a mechanism for the increased turnover observed for a number of recombinant mutant forms of the enzyme related to the metabolic disorder phenylketonuria, when expressed in eukaryotic cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Bergen, Norway.
authors.forename: A P
authors.initials: AP
authors.lastname: Døskeland
authors.forename: T
authors.initials: T
authors.lastname: Flatmark
mesh_terms: D000818:Animals; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D008114:Liver Neoplasms, Experimental / Q000201:enzymology; D046911:Macromolecular Substances; D008297:Male; D010651:Phenylalanine Hydroxylase / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D017384:Sequence Deletion; D013379:Substrate Specificity; D013737:Testis / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D011994:Recombinant Proteins; D014452:Ubiquitins; D010651:Phenylalanine Hydroxylase; D044767:Ubiquitin-Protein Ligases; D008025:Ligases