Which of the following is NOT a protease inhibitor?

• A. A1-AT
• B. A1-ACT
• C. A2-MG
• D. Albumin

Answer: (D)

Protease inhibitors are molecules that block the action of proteases, enzymes that break down proteins. In blood, several proteins act as inhibitors: alpha-1 antitrypsin neutralizes neutrophil elastase, protecting tissues; alpha-1 antichymotrypsin inhibits chymotrypsin-like proteases; alpha-2 macroglobulin traps a broad range of proteases and prevents them from digesting other proteins. Albumin, while the most abundant plasma protein with roles in maintaining oncotic pressure and transporting substances, does not inhibit proteases. Therefore, Albumin is not a protease inhibitor.