The termination of heparin activity by Protamine sulfate is the result of

• A. a chelating action
• B. inhibition of gastrointestinal absorption of Heparin
• C. prothrombin-like activity of Protamine
• D. an acid-base interaction

Answer: (D)

Protamine sulfate inactivates heparin mainly through an ionic, acid-base type interaction. Protamine is highly positively charged due to its arginine-rich structure, while heparin is intensely negatively charged because of many sulfate groups. When they meet, opposite charges attract and form a stable complex, neutralizing heparin's ability to boost antithrombin III and thereby abolishing its anticoagulant effect. This is not about chelating metals, interfering with absorption, nor mimicking prothrombin; it’s the charge-based binding that shuts down heparin’s activity.