An examination of the allosteric behavior of certain mutants of E. coli phosphofructokinase /
Traditionally, allosteric and cooperative behavior has been explained in terms of the two-state model, either in its concerted or its sequential formulation. There are many excellent features of the two-state model: its simplicity; its intuitive ease; the universal nature of its predictions; the co...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2003.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=765218931&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Traditionally, allosteric and cooperative behavior has been explained in terms of the two-state model, either in its concerted or its sequential formulation. There are many excellent features of the two-state model: its simplicity; its intuitive ease; the universal nature of its predictions; the consistency between the two-state assumption and assumptions about ligand binding. Unfortunately, the two-state assumption fails to account for many observed features of allosteric or cooperative behavior. Such phenomena as reciprocity, multiple modes of activation or inhibition, negative cooperativity, and inversion of allosteric effect with temperature or pH have all been documented, and are not easily explained by the various formulations of the two-state model. Thus, an alternative explanation of the structural nature of allostery is necessary. In order to address this issue, the enzyme E. coli phosphofructokinase (EcPFK) was selected for study. This enzyme displays allosteric activation by its product MgADP, allosteric inhibition by the penultimate product of the glycolysis pathway PEP, as well as positive cooperativity in the binding of the substrate F6P. Seven mutations were made in the core of the enzyme with the intention of perturbing one or more of the allosteric interactions. In the second chapter, it is shown that some of these mutations invert the signs of the enthalpy and entropy of MgADP/F6P activation. In the third chapter, given that the four interactions between MgADP and F6P are independent of one another in wild-type E. coli phosphofructokinase, the same interactions are shown to be independent in the presence of the enthalpy affecting mutation A179G. Similarly, it is shown that the effect upon the enthalpy in the A179G tetramer might come from an alteration in the F6P cooperativity. In the fourth chapter, it is shown that MgADP/F6P activation and PEP/F6P inhibition are transmitted independently of one another. In concluding, an alternative model is proposed that can explain these phenomena as well as the other documented phenomena of allostery and cooperativity. This model is predicated upon a current understanding of the nature of ligand binding, as set forth in the introduction to this work. |
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| Item Description: | Vita. "Major Subject: Biochemistry". |
| Physical Description: | xi, 118 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 110-117). |