Question

Pyruvate Kinase, an allosteric enzyme, accelerates the conversion of phosphoenolpyruvate to pyruvate.

1) Draw curves describing the way the speed of the reaction depends on the concentration of substrate, both in the presence of allosteric effectors (activating and inhibiting), and without effectors.

2) Explain the molecular mechanism by which each of the effectors influences the link between the activity of an enzyme and the concentration of the substrate, both according to the concerted model and the sequential model.

3) Does the shape of the curve hint at the structure of the enzyme in question? What do you base your thoughts on? Be detailed in your answer.

Answer 1

Answer:                    This question i have to write pointswise,because it's easy to understand you...

1):

• As Pyruvate kinase is an allosteric enzyme so it has two sites one is for the activity and other for the regulation.
• If an activator binds to the regulating site than the enzyme is upregulated and shows sigmoidal curve and if an inhibiting effector bind to the regulatory site than we got inhibiting curve.
• Without any effectors the graph is normal just like any enzyme. All the three graphs are shown below:

2):

• .Since Pyruvate kinase is an allosteric tetrameric enzyme so it can either exist in Relaxed(R) state or in Tensed(T) state.
• Relaxed form is enegetically more favourable form as compared to T state.
• According to concerted model enzyme can exist in either two state and effector binding to the subunit causes its conformational change and it can also influence the neighboring subunit.
• If the effector is an activator then it will increase the affinity of subunits for the activator and the last subunit has the highest affinity for the activator and this leads to the conformational change from T state to R state and so the activity of the enzyme increases.
• But if the inhibitor binds to the regulatory site of the subunit then it will reduce the affinity of the neighboring subunits for effectors and the last subunit has the lowest affinity and due to this there is decrement in the activity of the enzyme(Pyruvate kinase in this case).

3):

• No the shape of the curve does not hint at the structure of the enzyme because the curve only tells us about the Km(concentration at which half of the maximum velocity can achieved)
• and how an effector going to affect the Km of that particular enzyme.
• From the curve we can also check that the given effector is an activator or an inhibitor and we can also get some idea about the total subunits present on that particular enzyme by analyzing the changes of activity due to effectors(both type) and without any effector.
• But as i was saying we cannot predict the structure of the enzyme because information is not that sufficient.

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