205 Cooperativity and Allostery

Question 1

What is non-cooperative substrate binding?

Answer 1

This means that if you have a protein w/two or more active sites (e.g., dimeric protein), then the binding of the substrate at 1 site does not affect the activity at site 2 (vice versa). Each site is independent and it is like having two separate enzymes.

Question 2

Non-cooperative substrate binding fits what type of graph/function?

Answer 2

hyperbolic function/curve . There is a steep initial increase in reaction rate with increasing substrate concentration but as the substrate concentration increases, the rate of increase in velocity decreases until the rate no longer changes w/increasing [S], when the enzyme is saturated w/substrate

Question 3

What is the non-michaelis kinetic cooperative ligand binding?

Answer 3

The v0 vs. [S] curve is “S” shaped or sigmoidal. At low substrate concentrations, the velocity does not change appreciably. As [S] increases, the rate of change of velocity constantly increases and then decreases as the enzyme approaches saturation with substrate. This type of curve suggests that the binding of substrate at site 1 can affect the bindng of substrate at site 2. I.e., the active sites in a multimeric enzyme do communicate with one another. This is “allostery” (= “other site”), and although this usually arises from protein quaternary structure, not all proteins with quaternary structure show allosteric kinetics.

Question 4

When do allosteric interactions occur?

Answer 4

when a molecule binds to a protein and alters its biological activity

Question 5

What is the role of allosteric effectors ?

Answer 5

• allosteric effectors bind to a site separate from the active or functional site
• allosteric effectors (normally) perturb the quaternary structure of the protein

Question 6

What is the difference between a positive effector and negative effector?

Answer 6

A positive effector (or modulator) increases the biological activity while a negative one decreases biological activity

Question 7

What is homotropic?

Answer 7

when a substrate and effector are the same molecule but it binds at 2 separate sites

Question 8

What is heterotropic?

Answer 8

when substrate and effector are different molecules

Question 9

What is a classic allosteric enzyme?

Answer 9

aspartate transcarbamoylase (ATCase)