In drug transport, which protein predominantly binds drugs under acidic conditions?

• A. Acid-Glycoprotein
• B. Albumin
• C. Transferrin
• D. Haptoglobin

Answer: (A)

The key idea is how pH affects drug binding to plasma proteins. Alpha-1-acid glycoprotein is the main binder for basic (positively charged) drugs, and its affinity for these drugs increases in acidic conditions. When the environment is acidic, basic drugs become more protonated and interact more strongly with the negatively charged sites on acid glycoprotein, making it the predominant binding partner under those conditions. Albumin mainly handles many acidic drugs and is less involved with basic drugs at low pH. The other proteins have roles outside drug binding (for example, transferrin transports iron and haptoglobin binds free hemoglobin), so they’re not the primary drug binders in this acidic scenario.