Reactions of O-acyl-L-serines with tryptophanase, tyrosine phenol-lyase, and tryptophan synthase |
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| Authors: | R S Phillips |
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| Affiliation: | 1. Department of Clinical Pharmacy, Institute for Research and Medical Consultations (IRMC), Imam Abdulrahman Bin Faisal University, P.O. Box 1982, Dammam 31441, Saudi Arabia;2. Department of Chemistry, COMSATS University Islamabad, Abbottbad Campus 22060, Pakistan;3. Atta-ur-Rahman Institute for Natural Product Discovery, Universiti Teknologi MARA, Puncak Alam 40450, Malaysia;4. Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam 42300, Malaysia;5. UoN Chair of Oman’s Medicinal Plants and Marine Natural Products, University of Nizwa, P.O. Box 33, Birkat Al Mauz, Nizwa 616, Oman;1. State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China;2. School of Life Science, Liaoning Normal University, Dalian 116081, China;3. Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China;1. Ferrier Research Institute, Victoria University of Wellington, 69 Gracefield Rd, Lower Hutt 5040, New Zealand;2. Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA;3. Callaghan Innovation Ltd, Gracefield Rd., PO Box 31-310, Lower Hutt 5040, New Zealand;1. Biofilm Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB, Canada;2. Imperial – Sarnia Technology Applications & Research, Sarnia, ON, Canada |
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| Abstract: | The reactions of tryptophanase, tyrosine phenol-lyase, and tryptophan synthase with a new class of substrates, the O-acyl-L-serines, have been examined. A method for preparation of O-benzoyl-L-serine in high yield from tert.-butyloxycarbonyl (tBoc)-L-serine has been developed. Reaction of the cesium salt of tBoc-L-serine with benzyl bromide in dimethylformamide gives tBoc-L-serine benzyl ester in excellent yield. Acylation with benzoyl chloride and triethylamine in acetonitrile followed by hydrogenolysis with 10% palladium on carbon in trifluoroacetic acid gives O-benzoyl-L-serine, isolated as the hydrochloride salt. O-Benzoyl-L-serine is a good substrate for beta-elimination or beta-substitution reactions catalyzed by both tryptophanase and tyrosine phenol-lyase, with Vmax values 5- to 6-fold those of the physiological substrates and comparable to that of S-(o-nitrophenyl)-L-cysteine. Unexpectedly, O-acetyl-L-serine is a very poor substrate for these enzymes, with Vmax values about 5% of those of the physiological substrates. Both O-acyl-L-serines are poor substrates for tryptophan synthase, measured either by the synthesis of 5-fluoro-L-tryptophan from 5-fluoroindole and L-serine catalyzed by the intact alpha 2 beta 2 subunit or by the beta-elimination reaction catalyzed by the isolated beta 2 subunit. With all three enzymes, the elimination of benzoate appears to be irreversible. These results suggest that the binding energy from the aromatic ring of O-benzoyl-L-serine is used to lower the transition-state barrier for the elimination reactions catalyzed by tryptophanase and tyrosine phenol-lyase. Our findings support the suggestion (M. N. Kazarinoff and E. E. Snell (1980) J. Biol. Chem. 255, 6228-6233) that tryptophanase undergoes a conformational change during catalysis and suggest that tyrosine phenol-lyase also may undergo a conformational change during catalysis. |
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