The self-association of chorismate mutase/prephenate dehydratase from Escherichia coli K12 |
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Authors: | Graham S Baldwin Geoff H Mc Kenzie Barrie E Davidson |
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Institution: | Russell Grimwade School of Biochemistry, University of Melbourne, Parkville, Victoria, 3052, Australia |
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Abstract: | The state of association of chorismate mutase/prephenate dehydratase (EC 5.4.99.5/ 4.2.1.51) from E. coli K12 has been studied using ultracentrifugal techniques. The smallest species inferred is a dimer of molecular weight 73,000–84,000, with a of 5.02 S at pH 8.2, I = 0.013 M. This species undergoes a concentration-dependent self-association which results in an equilibrium mixture of dimer, tetramer, and probably octamer, with a Mr of 164,000 at an enzyme concentration of 8.0 mg/ml under the same conditions. Addition of the feedback inhibitor phenylalanine (2 mm) or increase in ionic strength (I = 0.40 M), or a decrease in pH to 7.4 displaces this equilibrium toward the higher-molecular-weight forms of the enzyme, resulting in Mr values of 273,000, 254,000, and 257,000, respectively. This behavior partially explains the allosteric kinetics and inhibitor binding observed previously with this enzyme. |
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Keywords: | Address reprint requests to Dr G S Baldwin Ludig Institute for Cancer Research Post Office Royal Melbourne Hospital Parkville Victoria 3050 Australia |
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