Question

A purified protein has a molecular mass of 360 kDa when measured by size exclusion chromatography. When analyzed by gel electrophoresis in the presence of SDS, three bands are observed, with molecular masses of 160, 140, and 60 kDa. When gel electrophoresis is carried out in the presence of SDS and dithiothreitol three bands are once again observed, with molecular masses of 140, 80, and 60 kDa. What is the subunit composition of the protein?

Answer 1

The actual size of protein is 360 kd.

But this single protein have multiple subunits. That is why the gelelectrophoresis have multiple bands.

The band size of the protein is: 160+140+60= 360

with dithiothritol: 140 and 60 kd subunit is same. but the subunit of size 160 also have 2 units of 80 kd which is obtained by dithiothritol.

Proteins have multiple subunits which are linked together by various bonds.

By the use of chemicals these bonds are broken down and subunits was seperated.

SDS breaks all bonds like electrostatoc, vander wals interaction but not disulfied bond.

Dithiothritol breaks disulfied bond: means we can say that subunit 80 is linked with onother 80kd subunit by disulfied bond which is not broken by SDS.