In serum protein electrophoresis, when a buffer solution of pH 8.6 is used, which of the following characterizes the proteins?

In serum protein electrophoresis, when a buffer solution of pH 8.6 is used, which of the following characterizes the proteins?

• A. Exhibit net negative charge
• B. Exhibit net positive charge
• C. Exhibit charge neutrality
• D. Migrate toward the cathode

Answer: (A)

The key idea is how a protein’s charge depends on pH relative to its isoelectric point. At pH 8.6, most serum proteins are above their pI, so they lose protons and carry a net negative charge. That negative charge is what electrophoresis separates by, and it explains why the proteins are characterized as having a net negative charge at this pH. In this setting, moving toward the cathode would require a net positive charge, which isn’t the case here, while neutral charge would occur near the protein’s isoelectric point.

The key idea is how a protein’s charge depends on pH relative to its isoelectric point. At pH 8.6, most serum proteins are above their pI, so they lose protons and carry a net negative charge. That negative charge is what electrophoresis separates by, and it explains why the proteins are characterized as having a net negative charge at this pH. In this setting, moving toward the cathode would require a net positive charge, which isn’t the case here, while neutral charge would occur near the protein’s isoelectric point.