Phosphofructokinase (PFK-1) is a glycolysis regulatory enzyme. It catalyzes the
ID: 280846 • Letter: P
Question
Phosphofructokinase (PFK-1) is a glycolysis regulatory enzyme. It catalyzes the reaction of phosphorylation of fructose-6-phosphate, according to the reaction
In this reaction, ATP acts as both the substrate and modulator. The following picture represents the kineticts of PFK-1.
a) Identify the kinectis of PFK-1. Justify your answer.
b) Explain why this enzyme does not follow the kinectics of Michaelis-Menten.
c) In the case of increased ATP concentration, what is the behavior of this enzyme, according to the Michaelis-Menten model?
d) In the case of increase ATP concentration, what is the behavor of this enzyme, according to the kinects represented in the picture?
Fructose 6 phosphate + ATP + Fructose 1,6 biphosphate + ADPExplanation / Answer
a) PFK-1 is an important enzyme which regulates the rate-limiting step in glycolysis. It is energy consuming enzyme utilises ATP to phosphorylate the substrate fructose 6-phosphate into fructose 1-6 bisphosphate. The enzyme velocity is generally depended by its substrates, in phosphofructokinase the enzyme velocity and rate of reaction is depended by the fructose6-phosphate. The phosphofructokinase activity increased by increasing concentration of fructose 6-phosphate(shown in the graph above).
But the other substrate ATP acts in a different way than the fructose6-phosphate in this enzyme kinetics. Increase in the ATP concentration in turns decreases the rate of the reaction. It must be acting as an allosteric regulator for this enzyme. The ATP binding to the enzyme in the allosteric site may lead to conformational changes that result in the inhibition of the reaction. So high concentrations of ATP is showing a sigmoidal curve in enzyme kinetics.
B) According to Michaelis-Mentens, the rate of the reaction depends on its substrate concentration. But here in this scenario, the rate of reaction is reduced due to high ATP concentration. That means ATP is allosterically regulating the enzyme. The ATP low concentrations it may bind to active site of the enzyme to activate the reaction, but if the ATP concentration is higher than the optimum, then the ATP also binds to the allosteric site of the enzyme along with the active site, this makes conformational change in the enzyme results in inhibition of the reaction.
The glycolysis is an energy producing pathway which needs to proceed when the cell needs energy in the form of ATP. If the ATP levels are high in the cells then Glycolysis is no longer needed, so it will be inhibited at its rate-limiting step( commitment step in glycolysis). That's why low ATP levels are activating the enzyme and high ATP levels are decreasing the enzyme activity by binding at an allosteric site.
c) In case of increased ATP concentration, the enzyme velocity needs to be increased according to Michaelis-Mentens modal.
d) According to the pictorial representation above, the reaction velocity is decreased in case of increased concentration of ATP.