Question

A protein’s stability is often assessed by its ability to resist chemical denaturation. In a lab experiment, you decide to test the stability of a protein containing a disulfide bond.

a) Draw the denaturation profile of the protein and indicate its Cm. Label your axes. What does the shape of the curve indicate about the general phenomenon of protein unfolding?

b) On the same graph, draw the denaturation profile of the same protein if the pH of the buffer was shifted down two units. Indicate the Cm of the protein at this more acidic pH. Explain your reasoning.

Answer 1

a)

6 ko (685 685 60.5 60 pH 7O 605) 8.0

y is the physical parameter that is used for measuring the unfolding transitions.

The curves can be conveniently divided into three regions as follows :

• The pre transition region whcih shows how the physical parameter depends on the denaturant for a folded protein
• The transition region that shows the variation in the physical parameter as the unfolding occurs
• The post transition region which shows the dependence of the physical parameter on the denaturant for the unfolded protein.

b)As can be seen in the figure , The denaturation decreases if the pH is shifted down by 2 units because of the nature of Ricin ( the protein for which the above curves are drawn ) .