Equine leukocyte elastase inhibitor. Primary structure and identification as a thymosin-binding protein.

The primary structure of an elastase inhibitor located in the cytoplasm of leukocytes obtained from the equine species has been determined. By sequence comparison, the protein was found to be a member of the serpin family with strong identity to plasminogen activator inhibitor-2. In contrast to other serpins this protein contained no carbohydrate and had a blocked amino terminus. Preliminary evidence indicates that the inhibitor has the additional feature of being a thymosin beta 4-binding protein, since this polypeptide was always located in purified preparations of the protein. This suggests a physiological role for cytoplasmic elastase inhibitors in the thymosin beta 4-regulated rearrangement of the cytoskeleton of leukocytes.