A protein is analyzed by SDSPAGE and the calculated Mr is 10

A protein is analyzed by SDS-PAGE and the calculated Mr is 10% higher than was expected.
What might explain this?

A.This protein has relatively high pI.
B.This protein has a relatively low pI.
C.This protein has non-covalently associated prosthetic groups.
D.None of these.

Why is it C? I don’t understand.

Solution

In SDS page, the protein is denatured to primary structure from quaternary sructure. Then the SDS covers the polypeptide chain giving it an overall negative charge in a ratio of 1.2g SDS/g of protien. However, more often than expected their are deviations from this assumptiom and as a result a deviation in size/molecular weight estimation and mobility of the protien. A prosthetic group is a non-protein part which can be organic like glycans, lipids or inorganic like ions/metal. These prosthetic groups are not covered by SDS i.e. are not given a negative charge as the rest of the polypeptide chain due charge or sterric repulsion. These prosthetic groups cause an obstruction in the hydrphobic interaction between the protein and SDS, thereby causing an aberration in charge-to-mass ratio which is the bases of movement in the SDS page. The charge to mass is reduced causing an increase in relative Molecular Weight (MW) than the actual MW.