A protein isolated from a thermophilic bacterium shows a molecular weight of 160 kD when eluted from a size-exclusion chromatography column, but when the purified protein is run on an SDS-PAGE gel, a single band of 80 kD is observed. These results tell us that the protein is eluting from the size-exclusion column as a

as a dimer consisting of two identical monomers (80 kDa subunits) that are packed together via hydrophobic interactions

Explanation:

SDS-PAGE (sodium dodecyl sulphate–polyacrylamide gel electrophoresis), is an electrophoretic methodology used to separate proteins that have a molecular weight between 5 to 250 kDa. SDS is a well-known ionic detergent that is able to break hydrophobic interactions and hydrogen bonds. Moreover, size-exclusion chromatography is a filtration technique that separates molecules in solution according to their molecular size. In this case, SDS-PAGE showed that the target protein is composed of two identical subunits (monomers) of 80 kDa each, which were separated by the detergent and formed one single band in the SDS-PAGE gel.