Cassady sandbox1: Difference between revisions
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==Role in Glycolysis== | ==Role in Glycolysis== | ||
Glycolysis is the process of breaking down glucose to make pyruvic acid, which is used in anaerobic respiration or as one of the starting reactants in the citric acid cycle. The process releases some energy but more importantly paves the way for vast amounts of energy to be made through the citric acid cycle. After glucose has been phosphorylated and isomerized to Fructose-6-phospate, PFK begins its work. It phosphorylates the hydroxy group at the number one carbon, which was impossible in glucose. This second phosphorylation by PFK is important because it | Glycolysis is the process of breaking down glucose to make pyruvic acid, which is used in anaerobic respiration or as one of the starting reactants in the citric acid cycle. The process releases some energy but more importantly paves the way for vast amounts of energy to be made through the citric acid cycle. After glucose has been phosphorylated and isomerized to Fructose-6-phospate, PFK begins its work. It phosphorylates the hydroxy group at the number one carbon, which was impossible in glucose. This second phosphorylation by PFK is important because it sets up the six carbon compound to later become high energy. High energy compounds help to drive the endergonic processes of glycolysis through their own exergonic breakdown.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. Hoboken, NJ: Wiley, 2008. Print.</ref>. It is important then that PFK makes a bisphosphate compound, because eventually that molecule will be cut in half. Thus, after the action of PFK, the six-carbon compound can be broken into two high-energy three-carbon compounds, which are both ready to move onto the next steps of catabolism. Also, phosphorylating the F6P allows energy to be captured rather than lost as heat. | ||
==Structure== | ==Structure== | ||
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[[Image:Paint_image.JPG]] | [[Image:Paint_image.JPG]] | ||
PFK is regulated by ATP, AMP, ADP. While ATP binds at the active site equally well in both R and T states, it preferentially binds the allosteric site of the T state <ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. Hoboken, NJ: Wiley, 2008. Print.</ref> This preferential binding causes a shift from equilibrium of the two states, to a greater amount of T state <ref>PubMed:2136935</ref>, which decreases the affinity for F6P. Allosteric activator <scene name='Zach_Westrick_Sandbox/Allosteric_activator/2'>ADP</scene> also binds to allosteric site to increase the ratio of R state phosphofructokinase. As can be seen from the graph below, the plots for the activity of PFK are sigmoidal. This further demonstrates the cooperative nature of the enzyme. The initial binding of substrate to the enzyme is difficult, but once it | PFK is regulated by ATP, AMP, and ADP. While ATP binds at the active site equally well in both R and T states, it preferentially binds the allosteric site of the T state <ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. Hoboken, NJ: Wiley, 2008. Print.</ref> This preferential binding causes a shift from equilibrium of the two states, to a greater amount of T state <ref>PubMed:2136935</ref>, which decreases the affinity for F6P. Allosteric activator <scene name='Zach_Westrick_Sandbox/Allosteric_activator/2'>ADP</scene> also binds to the allosteric site to increase the ratio of R state phosphofructokinase. As can be seen from the graph below, the plots for the activity of PFK are sigmoidal. This further demonstrates the cooperative nature of the enzyme. The initial binding of substrate to the enzyme is difficult, but once it is bound and forces the change in state from T -> R, the other substrates bind much more easily. The graph also shows that adding ATP moves the plot right (ie decreases affinity for F6P), while adding AMP moves it to the left. | ||
[[Image:Inhib.jpg]] | [[Image:Inhib.jpg]] | ||
The system of regulation matches well with the function of PFK. When PFK is active, ATP is being produced down stream from it as | The system of regulation matches well with the function of PFK. When PFK is active, ATP is being produced down stream from it as further products are broken down more completely. Thus, when ATP levels are low and more needs to be made, the activity of PFK will be increased, because ADP will be in high concentration. The opposite holds true as well, because high ATP concentration inhibits protein activity. And yet, this explanation cannot completely account for the regulation of PFK, because the levels of ATP do not vary greatly enough between active and resting muscles. Another means of allosteric regulation must be found.<ref>Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. Hoboken, NJ: Wiley, 2008. Print.</ref> | ||
PFK's Km for ATP is .020mM and .032mM.<ref>PMID: 6233271</ref> | |||
==Additional Resources== | ==Additional Resources== | ||
