Question

with reducing agents A B A B (5pts) Protein A contains 2 polypeptide chains (1 of 75,000, I of 25,000) held together by disulfide bonds. Protein B contains 2 polypeptide chains (each -75,000) held together by hydrophobic interactions and electrostatic forces. On the SDS-PAGE gel to the right, sketch the ideal pattern you expect for each of these proteins in the absence and presence of reducing agents. (Use your text for help if you need it.) Explain briefly your logic. 150,000 100,000 65,000 50,000 35,000 25,000

Answer 1

The effect of reducing agents on proteins is the destruction of disulfide bonds which might be holding different substructures together. This happens because reducing agents reduce the cysteine residues that form the disulfide bonds, "destroying" them and impeding their formation. This is why only protein A will suffer from the effect of the reducing agent, and the whole structure with the MW of 100,000 will be split into the two chains of 75,000 and 25,000. Meanwhile, there should be no effect on protein B, which will be present as a 150,000 unit in both cases (pay no mind to the shape of the bands, it's just my sloppy drawing, what's important is their position!)

with reducing agents A B A B 150,000 100,000 65,000 50,000 35,000 25,000