title: Lysine241 of tyrosine hydroxylase is not required for binding of tetrahydrobiopterin substrate.
abstract: The lysine residues at positions 194 and 198 in phenylalanine hydroxylase have been shown to react with a photoaffinity label which is an analog of phenyltetrahydropterin (Gibbs, B. S., and Benkovic, S. J. (1991) Biochemistry 30, 6795-6802), in a manner suggesting that these lysine residues are involved in tetrahydrobiopterin binding. The related enzyme tyrosine hydroxylase has a lysine at position 241 which, given the 75% identity between its C-terminal 330 amino acids and those of phenylalanine hydroxylase, corresponds to lysine194 of phenylalanine hydroxylase. Site-directed mutagenesis was used to alter lysine241 of tyrosine hydroxylase to alanine. Steady-state kinetic parameters were measured for wild-type and K241A tyrosine hydroxylase. No kinetic parameter differed between the wild-type and K241A enzymes, including Vmax values, Michaelis constants for tetrahydrobiopterin, 6-methyl-tetrahydropterin, and tyrosine, and the inhibition constants for norepinephrine. These results show that lysine241 is not required for tetrahydrobiopterin binding to tyrosine hydroxylase.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843-2128.
authors.forename: S C
authors.initials: SC
authors.lastname: Daubner
authors.forename: P F
authors.initials: PF
authors.lastname: Fitzpatrick
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D007700:Kinetics; D008239:Lysine / Q000235:genetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D001708:Biopterins; D014446:Tyrosine 3-Monooxygenase; C003402:sapropterin; D008239:Lysine