Alkaline electrophoresis: which hemoglobin migrates slowest?

• A. Hgb A
• B. Hgb S
• C. Hgb C
• D. Hgb F

Answer: (C)

In alkaline electrophoresis the separation of hemoglobins is driven by their net negative charge at high pH. The more negative the molecule, the faster it moves toward the anode; the less negative (or more positive) the net charge, the slower it migrates.

Hb A has the normal, relatively high negative charge, so it travels the fastest. Hb S has a substitution that reduces negative charge (glutamic acid to valine), so it migrates more slowly than Hb A but not as slow as the variant with an even less negative charge. Hb C has glutamic acid replaced by lysine, which not only removes a negative charge but introduces a positive element, markedly reducing the net negative charge and causing it to move much more slowly. Hb F behaves similarly to Hb A in this system and does not slow as much as Hb C.

Thus, Hb C is the slowest migrating hemoglobin on alkaline electrophoresis.