Question

If insulin were treated with mercaptoethanol to break its disulfide bonds, and then the mercaptoethanol were removed so that disulfide bonds could reform, how many different ways could the two polypeptide cahins become linked to each other? (assuming that one or two disulfide bonds can form between the two chains)?

Can you show me how you got to the answer too? :)

Answer 1

In the structure of insulin there are 4 cys residues are present in the chain A and 2 in the chain B.Thus there are 4 x 2 = 8 possible methods to form a single cys-cys linkage.

Similarly There are 2 disulfide bonds there are four ways of forming the first bond and then three ways of forming the second bond as a result there are 4 x 3 =12 possible methods to form these two disulfide bonds.

Now count these all method to calculate the total ways of linking the chain A and B:

8 +12=20

Hence there are 20 different ways of linking the A and B chains through disulfide bonds If insulin were treated with mercaptoethanol to break its disulfide bonds, and then the mercaptoethanol were removed so that disulfide bonds could reform