Hemoglobin is a tetrameric protein made up of four subunits (two alpha and two beta subunits), so if you run hemoglobin on an SDS-PAGE gel, you are likely to see one band. SDS-PAGE, or sodium dodecyl sulfate polyacrylamide gel electrophoresis, is a method used to separate proteins based on their size and charge. The SDS in the name of the method refers to sodium dodecyl sulfate, which is a detergent that is used to denature and uniformly charge the proteins, making them more susceptible to separation by size.
In SDS-PAGE, proteins are loaded onto the gel and then subjected to an electric field, which causes them to migrate through the gel based on their size and charge. The larger, heavier proteins will migrate more slowly through the gel, while the smaller, lighter proteins will move more quickly.
Since hemoglobin is a tetrameric protein, it will have a single band on the SDS-PAGE gel, even though it is made up of four subunits. This is because the SDS coating completely denatures the protein and causes it to adopt a uniform charge and size, making it appear as a single entity on the gel. The size of the band will depend on the size of the hemoglobin tetramer, which is typically around 68 kDa.