Question

an allosteric enzyme that follws the concerted mechanism (MWC model) has T/R ratio of 300 in the absence of substrate.  Suppose that a mutation reversed the ratio.  How would this mutation affect the relationship between the rate of the reaction (V) and substrate concentration ([S])? Select all that apply.

The enzyme would be less active

The enzyme would likely follow Michaelis-Menten kinetics

The plot of V vs. [S] would be shaped like an S, sigmoidal

The enzyme would be mostly in the R form

The plot of V vs. [S] would be shaped like a hyperbola

Answer 1

Concepts and reason

Allosteric regulation is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme’s site and the site to which the effector molecule binds is known as the allosteric site. This often results in conformational change and the protein’s activity is enhanced by the effector and therefore it is referred to as allosteric activators.

Fundamentals

Allosteric effect can be explained by four models which include Concerted model, Sequential model, Morpheein model, and Ensemble model. However, most allosteric effects are explained by concerted model MWC model put forth by Monod, Wyman, and Changeux, or by the sequential model put forth by Koshland, Nemethy, and Filmer.

Both these models state that the enzyme subunits exists in either T (tensed) or R (relaxed) state and the relaxed subunit

Concerted model or MWC model or symmetry model states that the enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits i.e. all the active sites should be in the same state.

The relationship between the rate of reaction and the concentration of the substrate depends on the affinity of the enzyme for its substrate which is usually expressed as or the Michaelis-Menten constant. Due to the mutation, the entire enzyme exists in only one state either R or T state. Since R state is more stable, all of the enzyme would be in R state only.

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