Cassady sandbox1: Difference between revisions

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 has 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.

The system of regulation matches well with the function of PFK. When PFK is active, ATP is being produced down stream from it as glucose is eventually broken down 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, when ATP is in high concentration and inhibits protein activity. And yet, this explanation cannot completely account for the regulation of PFK, because the levels of ATP do not very 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>   

The PFK's Km for ATP is .020mM and .032mM.<ref>PMID: 6233271</ref>