Mechanism of phenylalanine regulation of phenylalanine hydroxylase. Export

@article{citeulike:2707474, abstract = {The mechanism of phenylalanine regulation of rat liver phenylalanine hydroxylase was studied. We show that phenylalanine "activates" phenylalanine hydroxylase, converting it from an inactive to active form, by binding at a true allosteric regulatory site. One phenylalanine molecule binds per enzyme subunit; it remains at this site during catalytic turnover and, while there, cannot be hydroxylated. Loss of phenylalanine from the site causes a loss of enzymatic activity. The rate of loss of activation is dramatically slowed by phenylalanine, which kinetically "traps" activated enzyme during relaxation from the activated to unactivated state. An empirical equation is presented which allows calculation of relaxation rates over a wide range of temperatures and phenylalanine concentrations. Kinetic trapping by phenylalanine is a novel effect. It was analyzed in detail, and its magnitude implied that phenylalanine activation involves cooperativity among all four subunits of the enzyme tetramer. A regulatory model is presented, accounting for the properties of the phenylalanine activation reaction in the forward and reverse directions and at equilibrium. Fluorescence quenching studies confirmed that activation increases the solvent accessibility of the enzyme's tryptophan residues. Physical and kinetic properties of purified phenylalanine hydroxylase from rat, rabbit, baboon, and goose liver were compared. All enzymes were remarkably alike in catalytic and regulatory properties, suggesting that control of this enzyme is similar in mammals and birds.}, address = {Department of Biological Chemistry, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.}, author = {Shiman, R. and Jones, S. H. and Gray, D. W.}, citeulike-article-id = {2707474}, citeulike-linkout-0 = {http://view.ncbi.nlm.nih.gov/pubmed/2365689}, citeulike-linkout-1 = {http://www.hubmed.org/display.cgi?uids=2365689}, day = {15}, issn = {0021-9258}, journal = {The Journal of biological chemistry}, keywords = {mammalian, pah, regulation}, month = {July}, number = {20}, pages = {11633--11642}, posted-at = {2008-04-23 13:36:17}, priority = {2}, title = {Mechanism of phenylalanine regulation of phenylalanine hydroxylase.}, url = {http://view.ncbi.nlm.nih.gov/pubmed/2365689}, volume = {265}, year = {1990} }

TY - JOUR ID - citeulike:2707474 L3 - citeulike-article-id:2707474 N2 - The mechanism of phenylalanine regulation of rat liver phenylalanine hydroxylase was studied. We show that phenylalanine "activates" phenylalanine hydroxylase, converting it from an inactive to active form, by binding at a true allosteric regulatory site. One phenylalanine molecule binds per enzyme subunit; it remains at this site during catalytic turnover and, while there, cannot be hydroxylated. Loss of phenylalanine from the site causes a loss of enzymatic activity. The rate of loss of activation is dramatically slowed by phenylalanine, which kinetically "traps" activated enzyme during relaxation from the activated to unactivated state. An empirical equation is presented which allows calculation of relaxation rates over a wide range of temperatures and phenylalanine concentrations. Kinetic trapping by phenylalanine is a novel effect. It was analyzed in detail, and its magnitude implied that phenylalanine activation involves cooperativity among all four subunits of the enzyme tetramer. A regulatory model is presented, accounting for the properties of the phenylalanine activation reaction in the forward and reverse directions and at equilibrium. Fluorescence quenching studies confirmed that activation increases the solvent accessibility of the enzyme's tryptophan residues. Physical and kinetic properties of purified phenylalanine hydroxylase from rat, rabbit, baboon, and goose liver were compared. All enzymes were remarkably alike in catalytic and regulatory properties, suggesting that control of this enzyme is similar in mammals and birds. IS - 20 JF - The Journal of biological chemistry SN - 0021-9258 AD - Department of Biological Chemistry, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033. EP - 11642 TI - Mechanism of phenylalanine regulation of phenylalanine hydroxylase. VL - 265 SP - 11633 KW - mammalian KW - pah KW - regulation AU - Shiman, R AU - Jones, SH AU - Gray, DW PY - 1990/07/15/ UR - http://view.ncbi.nlm.nih.gov/pubmed/2365689 ER -