1. Regulation of PFK-1 The effect of ATP on the allosteric enzyme PFK-1 is shown

Question

1. Regulation of PFK-1 The effect of ATP on the allosteric enzyme PFK-1 is shown below. For a given concentration of fructose 6-phosphate, the PFK-1 activity increases with increasing concentrations of ATP, but a point is reached beyond which increasing the concentration of ATP inhibits the enzyme.

(a) Explain how ATP can be both a substrate and an inhibitor of PFK-1. How is the enzyme regulated by ATP?

(b) In what ways is glycolysis regulated by ATP levels?

(c) The inhibition of PFK-1 by ATP is diminished when the ADP concentration is high, as shown in the illustration. How can this observation be explained?

Explanation / Answer

a. PKF1 is an allosteric enzyme which exist in both R and T states. PFK1 In R-state binds to ATP such that with the increasing binding efficiency a sigmoidal graph is attained; PFK bound with ATP facilitates the formation T-State which inhibits PFK . Next a stage come where no ATP could bind to PFK1 ; this stage is called saturation point at which T-state of enzyme get conformationally changed to R-state which is an active state of enzyme. Now this R-STATE have the binding effinity for ADP. As soon as ADP binds with PFK 1, binding efficiency keep on increasing. R-state is the active state of enzyme where it bind to its activator (ADP or AMP).

b. level of ATP in cells regulate glycolysis initiation. When cells get depleted of ATP, the level of glucose in blood increases. Glucose is positive regulator of hexokinase. so with an in crease in glucose level hexokinase will star glycolysis.

c. i have explained this in a-part, explanation is same. ADP is positive regulator of PFK1 by facilitating formation of R state ( an active state of enzyme), while ATP is negative regulator which facilitate T state, an inactive state of enzyme.

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