On electrophoresis at alkaline pH, which hemoglobin migrates the slowest?

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

Answer: (C)

At alkaline pH, hemoglobins migrate toward the anode with a speed that depends on their net negative charge. The Hb C variant has a substitution in the beta chain where a negatively charged glutamic acid is replaced by a positively charged lysine. This increases the positive/neutral character and reduces the overall negative charge of Hb C compared with normal Hb A. With less driving force toward the anode, Hb C moves more slowly, so it appears as the slowest migrator among the common variants on alkaline electrophoresis. Hb S also loses some negative charge due to its mutation, but not to the same extent, so its mobility is not as slow as Hb C. Hb F tends to occupy a different position altogether.