On cellulose acetate electrophoresis at pH 8.6, which hemoglobins are most likely indistinguishable due to similar mobilities?

• A. A1 and F
• B. A1 and A2
• C. S and F
• D. A1 and S

Answer: (B)

In alkaline cellulose acetate electrophoresis at pH 8.6, hemoglobin mobility is driven mainly by net charge. Hemoglobins A1 and A2 differ only in their globin chains (A1 has beta chains, A2 has delta chains), and at this pH their overall charges are very similar. That near-identical charge-to-mass ratio causes them to migrate at nearly the same rate, so they appear as indistinguishable bands on the gel.

This is why A1 and A2 are the pair most likely to be seen as a single band in this system. In contrast, Hb S (sickle) and Hb F (fetal) have different amino acid compositions that alter their charge, leading to distinct mobilities and separations under the same conditions.