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A2221 Sigma-Aldrich

Antithrombin III from human plasma

lyophilized powder, ≥95% (SDS-PAGE)

Synonym: Factor Xa inhibitor, Heparin cofactor



Biochem/physiol Actions

Serine protease inhibitor; Inhibitor of thrombin and activated factor X (Xa). Effective concentration equimolar with proteinase.


Not to be confused with thrombin antiserum.

Unit Definition

One unit is the activity present in 0.1 mL of normal human pooled plasma tested in the presence of 0.1 unit of heparin.

Physical form

Lyophilized from 20 mM Tris, pH 8.0

Safety & Documentation

Safety Information

NONH for all modes of transport
WGK Germany 
Flash Point(F) 
Not applicable
Flash Point(C) 
Not applicable


Certificate of Analysis (COA)

Please Enter a Lot Number

Certificate of Origin (COO)

Please Enter a Lot Number

Frequently Asked Questions

Which document(s) contains shelf-life or expiration date information for a given product?
If available for a given product, the recommended re-test date or the expiration date can be found on the Certificate of Analysis.
How do I get lot-specific information or a Certificate of Analysis?
The lot specific COA document can be found by entering the lot number above under the "Documents" section.
What is the specific activity of Antithrombin III from human plasma?
We do not have strict specifications for the specific activity of the A2221. It is typically in the range of 40-80 units per mg protein. The value is reported on the certificate of analysis for each lot.
What is the molecular weight for Antithrombin III from human plasma. Product A2221?
The molecular weight of Antithrombin III from human plasma is approximately53 kDa.
What is Antithrombin III from human plasma, Product A2221, soluble in?
The manufacturer has found it to be soluble in 50 mM Tris buffer with 150 mM sodium chloride.(No specific pH or concentration was provided.)
The Antithrombin III from human plasma, Product A2221, vial appears to be empty. What should I do?
What you are observing is normal for this product. Each vial has sub-milligram amounts in it (either 25 or 125 micrograms), which may not be visible. One should reconstitute the vial, and measure the absorbance at 280 nm to show that it does have protein present.
How do I find price and availability?
There are several ways to find pricing and availability for our products. Once you log onto our website, you will find the price and availability displayed on the product detail page. You can contact any of our Customer Sales and Service offices to receive a quote. USA customers: 1-800-325-3010 or view local office numbers.
What is the Department of Transportation shipping information for this product?
Transportation information can be found in Section 14 of the product's (M)SDS.To access the shipping information for this material, use the link on the product detail page for the product.
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Protocols & Articles


Plasma Derived Proteins and Enzymes

Despite their complexity, blood and plasma are abundant biological resources for the discovery of drug targets and biomarkers for human disease. It is estimated that plasma may contain as many as 40,...
BioFiles 2006, 1.5, 2.
Keywords: Applications, Gas chromatography, Type

Peer-Reviewed Papers


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