Question

Q1. Why is PFK important in the glycolysis pathway? What does it do within it's rate-limiting step? Think about the Committed, rate-limiting and reversible steps in this pathway.

Answer 1

Answer-

According to the given question-

• We know that Glycolysis occurs in the cytosol of the cell and convert glucose molecule into pyruvate, Gluconeogenesis occurs mainly in the liver, and responsible for providing the glucose when the amount of stored glycogen become exhausted. Gluconeogenesis is defined as the reverse process of Glycolysis. In Glycolysis seven enzymatic steps are reversible and three reactions are Exergonic and are irreversible, such as the reaction catalyzed by the enzyme phosphofructokinase – 1 or PFK-1, pyruvate kinase, and hexokinase.
• Phosphofructokinase – 1 enzyme is responsible for converting the fructose 6- phosphate into fructose 1, 6- bisphosphate while fructose 1,6-bisphosphate is converted to fructose 6-phosphate with the help of enzyme fructose 1,6- bisphosphatase or FBPase-1 in Gluconeogenesis.
• Glucose 6-phosphate has several fates, it can join the   Glycolysis, or pentose phosphate Pathway as well as glycogen synthesis. The reaction catalyzed by phosphofructokinase – 1 is irreversible and considered as rate-limiting steps of Glycolysis because the glucose will join the pathway of Glycolysis.
• phosphofructokinase – 1 is a complex enzyme and has substrate-binding sites, as well as several regulatory sites for binding of several allosteric activators as well as inhibitors. ATP is work as the substrate for phosphofructokinase – 1 but also end product of Glycolysis. When the concentration of ATP inside the cell is high which means that the rate of producing of ATP is very high than its consumption then the ATP is responsible for inhibiting the activity of phosphofructokinase – 1 by binding its allosteric site and lower the binding affinity of phosphofructokinase – 1 for the substrate fructose 6-phosphate .
• Adenosine Diphosphate or ADP, as well as Adenosine monophosphate or AMP, increases inside the cell when the concentration of ATP decreases and act allosterically on the enzyme phosphofructokinase – 1 and reverse the inhibition by ATP on the enzyme phosphofructokinase – 1.
• So the activity of phosphofructokinase – 1 is increases when Adenosine Diphosphate or Adenosine monophosphate accumulates inside the cell and becomes lower when ATP accumulates. Citrate also works as an allosteric regulator of phosphofructokinase – 1. high concentration of citrate increases the effect of ATP on phosphofructokinase – 1 and reduces the glucose flow through glycolysis.