What method is used to detect changes in molecular weight due to complex formation in chemical cross-linking?

SDS-PAGE, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is the method that is used to detect changes in molecular weight due to complex formation in chemical cross-linking. This technique separates proteins based on their molecular weight, allowing for the observation of shifts in band position indicative of complex formation.

When cross-linking occurs, proteins that are initially separate can form larger aggregates. SDS-PAGE denatures proteins and gives them a uniform negative charge based on their size, which means when these proteins are loaded onto the gel and subjected to an electric field, they migrate according to their molecular weight. If complex formation increases the size of the protein, it will move more slowly through the gel, resulting in a higher molecular weight band. This shift can be compared to a control sample to assess the extent of complex formation.

Other methods mentioned, such as gel filtration chromatography, primarily separate proteins based on size in a different context, while Western blotting is typically used for specific protein detection after separation, and affinity purification is used for isolating specific proteins. These methods do not provide the direct analysis of changes in molecular weight due to complex formation as efficiently as SDS-PAGE does in this context.