Chorismate mutase-prephenate dehydrogenase from Escherichia coli: cooperative effects and inhibition by L-tyrosine |
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| Authors: | R I Christopherson |
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| Affiliation: | 1. Dipartimento di Scienza e Tecnologia del Farmaco, Università degli Studi di Torino, Turin, Italy;2. Department of Mathematics and Statistics, University of Strathclyde, Glasgow, UK;3. Dipartimento di Matematica “Giuseppe Peano”, Università degli Studi di Torino, Turin, Italy;4. Dipartimento di Informatica, Università degli Studi di Torino, Turin, Italy;1. Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, School of Pharmacy, Shanghai Jiao Tong University, Shanghai 200240, China;2. Institute of Interdisciplinary Sciences, Shanghai University of Traditional Chinese Medicine, Shanghai 201203, China;3. School of Pharmacy, Second Military Medical University, Shanghai 200433, China;1. Key Laboratory of Targeted Intervention of Cardiovascular Disease, Collaborative Innovation Center for Cardiovascular Disease Translational Medicine, Department of Pathophysiology, Nanjing Medical University, Nanjing, China;2. Institute of Biomedical Research, Liaocheng University, Liaocheng, China;3. Department of Medicine, Jiangsu Health Vocational College, Nanjing, China;4. Cardiovascular Disease and Research Institute, Affiliated Hospital of Hainan Medical College, Haikou, Hainan, China |
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| Abstract: | The effects of a variety of structural analogs of L-tyrosine on the mutase and dehydrogenase activities of hydroxyphenylpyruvate synthase have been investigated. From these studies it is concluded that the alpha-NH3+ alpha-COO-, and the 4-OH groups are essential for binding of L-tyrosine as an inhibitor of the dehydrogenase and that the L configuration is also essential. Dixon plots for inhibition of the dehydrogenase activity by some of these analogs were nonlinear and could be described by a velocity equation that is the ratio of quadratic polynomials (a 2/1 function). Dixon plots for inhibition of the mutase by prephenate at low concentrations of chorismate could also be described by a 2/1 function, but at low concentrations of prephenate chorismate acts as an apparent hyperbolic activator of the dehydrogenase activity. Up to concentrations of 300 microM, L-tyrosine activates the mutase but acts as a potent inhibitor of the dehydrogenase. Such data for the dehydrogenase could not be described by a 2/1 function in 1/[prephenate] but could be fitted to the Hill equation with increasing concentrations of L-tyrosine in the presence of 1.0 mM NAD yielding increasing values for the Hill number (n): in the absence of L-tyrosine, n = 1.6 +/- 0.1; at 150 microM L-tyrosine, n = 2.1 +/- 0.1; at 300 microM L-tyrosine, n = 2.3 +/- 0.4. L-Tyrosine bears a close structural resemblance to both prephenate and hydroxyphenylpyruvate, and evidence is presented which is consistent with L-tyrosine acting as a competitive inhibitor with respect to prephenate of the dehydrogenase. |
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