Protein X is a protein that is composed of four subunits of equal size--alpha, beta, delta, and gamma--that are bound by either noncovalent interactions or disulfide bridges. Only the beta and delta subunits are bound to each other by disulfide bridges. How many bands would you expect to see in an SDS PAGE experiment in which beta-mercaptoethanol, a reducing agent, is used?
a. 1b. 4c. Noned. 2e. 3

The given protein in the question proteib X contain four subunits of equal size alpha,beta,delta and gamma which are bound by either noncovalent interactions or disulfide bridges and only beta and delta subunits are bound to each other by disulfide bridges.

As a result when the protein will undergo fragmentation it will generate 3 bands because the interaction that is present between alpha and beta subunit will break resulting in the formation of 2 bands. Now the most important fact is that the beta subunit is linked to delta subunit by di sulfide bond so when betamarcaptoethanol will act on protein X it will break the disulsulfide bond present between the beta and delta subunit to reduce both the subunit.

Finally the interaction that is present between delta subunit and gamma subunit will be broken down to release the delta subunit which will form a single band during SDS PAGE..