Identification of the second alpha-2-antiprotease of equine serum as antithrombin III.

This research article established that the second alpha-2-antiprotease found in horse plasma is identical to antithrombin III, a protein inhibiting the activity of certain enzymes related to blood clotting.

Object of Study and Initial Findings

• The researchers focused on the alpha-2-protease inhibitor, a protein with a molecular weight of 65,000 daltons, found in horse plasma. This protein was also discovered as a contaminant in alpha-1-isoinhibitor isolates in earlier research.
• Through purification processes, they identified this protein as antithrombin III.

Composition and Function of the Inhibitor

• The SDS polyacrylamide gel electrophoresis test showed that the inhibitor, antithrombin III, is composed of a single polypeptide chain.
• The function of the inhibitor was further analyzed. The results showed that it was only effective against the enzymes trypsin and thrombin, both of which play crucial roles in digestion and blood clotting, respectively.

Serological Reaction Analysis

• The article stated that a cross-reaction existed between the inhibitor (antithrombin III) and the antiserum to human antithrombin III – it means the horse antithrombin III triggers an immune response when exposed to the human form of antithrombin III.
• However, this reaction was not reciprocal. When human antithrombin III was exposed to an antiserum derived from the horse antithrombin III isolate, there was no reaction. This observation aligned with earlier research findings by Kurachi et al.