Question

Phosphofructokinase-1

what are some ways Phosphofructokinase-1 is like hemoglobin?

why are these similarities important?

what are the functions of all of the allosteric regulators, how do they regulate the activity of Phosphofructokinase-1?

in what way does ATP inhibit Phosphofructokinase?

Answer 1

Phosphofructokinase-1 is like hemoglobin?

1. Phosphofructokinase-1 has a tetrameric structure just like hemoglobin, which is the active form of PFK-1.
2. As like hemoglobin, its association is pH-dependent, at high pH, it forms tetramer. Where in Hb high pH promotes the binding of the monomer form to dimer and so on to form a tetramer. High pH facilitates the binding of O2 to Hb and at low pH, H+ ions reduce the affinity of O2 binding.
3. As iron promotes the Hb binding similarly, Mg2+ promotes PFK-1 binding to tetrameric form.
4. PFK shows allosteric inhibition through ATP and 2,3-bisphosphoglycerate as like Hb.

What are the functions of all of the allosteric regulators, how do they regulate the activity of Phosphofructokinase-1?

1. Allosteric enzymes are multisubunit enzymes that do not follow the Michaelis Menten Equation. Allosteric regulation denotes the regulation of an enzyme by binding to an effector molecule at a site other than the active site of the enzyme. this site is different than the active site is known as an allosteric site.
2. In phosphofructokinase, negative allosteric regulation can also be observed. Here ATP acts as an allosteric regulator that regulates the concentration of phosphofructokinase.
3. phosphofructokinase catalyzes the conversion of Fructose-6-Phosphate into Fructose 1-6 Biphosphate. ATP is a substrate as well as an inhibitor of phosphofructokinase-1.

in what way does ATP inhibit Phosphofructokinase?

If present in normal conditions it facilitates the activity of phosphofructokinase-1. But if present in excess, so it starts inhibiting  phosphofructokinase-1 by a feedback negative mechanism. It is an obvious fact because PFK-1 works in the process of Glycolysis to make ATP, but if ATP is in excess we need to stop the process and this step is catalyzed by PFK-1 is committed-step, so regulation needs to occur on this step.