regglyc - Regulation of Glycolysis Bryant Miles Because the...

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Regulation of Glycolysis Bryant Miles Because the principle function of glycolysis is to produce ATP, it must be regulated so that ATP is generated only when needed. The enzyme which controls the flux of metabolites through the glycolytic pathway is phosphofructokinase (PFK-1). PFK-1 is an allosteric enzyme that occupies the key regulatory position for glycolysis. PFK-1 has a tetrameric enzyme composed of four identical subunits. Like other allosteric proteins (hemoglobin) and enzymes (ATCase) the binding of allosteric effectors and substrates is communicated to each of the active sites. Quaternary changes are concerted and preserve the symmetry of the tetramer. PFK-1 has two sets of alternative interactions between subunits which are stabilized by hydrogen bonds and electrostatic interactions. The two set of conformations are called the T and R states. These two conformational states are in equilibrium: T R I. ATP feedback inhibition . The function of the glycolytic pathway is to generate ATP. ATP is both a substrate and an allosteric inactivator. The enzyme has two binding sites for ATP. One is the substrate binding site and the other one is an inhibitory site. The PFK-1 substrate binding site binds ATP equally well in both the T and R states. The inhibitory ATP binding site only binds ATP when the enzyme is in the T conformation. The other substrate fructose-6-phosphate binds only to the R state. High concentrations of ATP shift the equilibrium towards the T conformation which decreases the affinity of the enzyme for F-6-P. II. AMP reverses inhibition . AMP reverses the inhibition due to high concentrations of ATP. AMP binds preferentially to the R state of PFK. This is important the concentration of ATP drops only 10 % during vigorous exercising. AMP concentration levels in the cell can rise dramatically due to the enzymatic activity of adenylate kinase. 2ADP ATP + AMP 2 ] [ ] ][ [ ' ADP AMP ATP K eq = The steady state concentration of ATP in the cell is 10 times greater than the concentration of ADP, and 50 times the concentration of AMP. As a result of the activity of adenylate kinase, a 10% decrease in the concentration of ATP results in 400 % increase in the concentration of AMP.
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This note was uploaded on 04/11/2010 for the course BICH bich 411 taught by Professor Bryantmiles during the Spring '10 term at Texas A&M.

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regglyc - Regulation of Glycolysis Bryant Miles Because the...

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