Question

The alternating units in Heparin is

• A. Sulfated glucosamine and sulfated iduronic acid
• B. L-iduronic acid and N-Acetylgalactosamine
• C. D-Glucuronic acid and N-Acetylglucosamine
• D. D-Glucuronic acid and Galactose

Hint:

Heparin stands out as the most highly sulfated biomolecule in the human body.
Look for the option that emphasizes "sulfated" groups on both the amino sugar and the uronic acid.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Heparin is a highly sulfated glycosaminoglycan (GAG) that is widely used as a clinical anticoagulant.
It consists of repeating, unbranched disaccharide units containing an amino sugar and a uronic acid.

Step 2: Detailed Explanation:
The polymeric chain of heparin is made of alternating disaccharide units.
These units consist of:
A glucosamine derivative (typically $\alpha$-D-glucosamine), which is highly sulfated at both the nitrogen and oxygen positions (N-sulfated or O-sulfated).
A uronic acid residue, which is predominantly sulfated L-iduronic acid ($\alpha$-L-iduronic acid 2-sulfate, comprising roughly $90\%$), with a smaller fraction consisting of D-glucuronic acid.
This high degree of sulfation gives heparin a very high negative charge density, which is critical for its binding to antithrombin III and its subsequent anticoagulant activity.

Step 3: Final Answer:
The primary repeating disaccharide unit of heparin consists of sulfated glucosamine alternating with sulfated iduronic acid.