Applying two independent criteria reduces the chance that proteins with a similar property remain together. Isoelectric point distinguishes proteins by their focusing behavior, while molecular mass provides a second sorting axis. The combined spot map therefore gives a more informative profile of a complex mixture than either property considered alone.
The first dimension organizes proteins by isoelectric point before sodium dodecyl sulfate treatment prepares them for mass-based separation. This sequence preserves the value of both measurements in a single gel pattern: proteins are positioned by their isoelectric points along one axis and by molecular mass along the other, supporting more specific comparisons.
Comparing spot patterns between samples can reveal differences in the presence, position, or apparent abundance of resolved proteins. A changed pattern may therefore indicate altered expression or a post-translational modification associated with a protein. The gel functions as a comparative profile that helps identify molecular differences for further investigation.
A sample is first subjected to isoelectric focusing, then treated with sodium dodecyl sulfate, and subsequently separated in a second polyacrylamide gel dimension according to molecular mass. After electrophoresis, the resulting spots can be compared across samples or selected for downstream protein identification, including mass spectrometry.
The method is useful when a protein mixture is sufficiently complex that a single separation property would provide limited profiling information. Its two-dimensional pattern supports comparative analysis between samples, including examination of expression changes and post-translational modification. In proteomics workflows, selected spots can also provide targets for further identification.
The separated spots create defined targets that can be selected from the gel for subsequent analysis. This organization is valuable because a complex mixture is converted into a spatially arranged protein profile, allowing investigators to focus identification efforts on spots of interest rather than treating the entire mixture as one unresolved sample. Mass spectrometry is one downstream option.