Question

You watch as PFK-1 releases you and awestruck you watch as another molecule binds to PFK-1. However, it binds to a site other than the active site. The PFK-1 active site morphs and completely changes; the enzyme almost seems sick and although it tries to bind another fructose 6-phosphate, it cannot. A classmate sitting next to you whispers, “We barely made it; you see that molecule that bound to the allosteric site, that’s phosphoenolpyruvate (PEP), we’ll meet it later. It’s one powerful dude but when it accumulates it majorly downregulates glycolysis.” You shake your head and realize what is going on.

1. What type of regulation did we just witness?

Answer 1

biological systems are tight regulated for optimal activity. these regulations are made possible through interacting proteins in the form of receptor and ligand and other forms can also be there. a receptor/ protein will have a active binding site to which the molecule of interest often called as substrate binds. the binding of substrate will trigger a esposnse and will lead to a cascade of events. but in the protein there is another pocket where someother molecule can bind. when some molecule bind here it will disrupot the binding sitea nd hampers the uptake of the substrate such regulation is called allosteric regulation and the binding site is called allosteric site.

in allosteric regulation , an allostere molecule will come and bind to the allosteric site making the shape of the active site to change and ends up in low uptake of the substrate. many drugs are allosteric targets of the proteins of interest. they generally downregulate the function of the protein.

PFk1 or phospho fructokinase is an enxyme which converes fructose 6 phosphate(F6P) to fructose 1-6 bisphosphate (F16BP)with the help of an ATP. phosphoenol pyruvate or PEP is the penultimate step precursor of glycolysis whcih forms pyruvate which is the end product of glycolysis. if the cell is actively converting the F6P to F16BP then the amount of PEP will keep on increasing. this can lead to toxicity and eventual cell death. PFk 1 is sensitive to PEP with a high Km value which means a large amaount of PEP is required for the binding of PEP to PFK.

as glycolysis proceeds the amount of PEP will keep on increasing(one glucose produces 2 PEP) when the threshold level of PEP concentration occours the PEP wil bind with the allosteric site and bring down the conversion of F6P toi F16BP and keeping the glycolysis in control.