Nomenclature
The protein was originally named "antitrypsin" because of its ability to covalently bind and irreversibly inactivate the enzyme trypsin in vitro. Trypsin, a type of peptidase, is a digestive enzyme active in the duodenum and elsewhere.
The term alpha-1 refers to the protein's behavior on protein electrophoresis. On electrophoresis, the protein component of the blood is separated by electric current. There are several clusters, the first being albumin, the second being the alpha, the third beta and the fourth gamma (immunoglobulins). The non-albumin proteins are referred to as globulins.
The alpha region can be further divided into two sub-regions, termed "1" and "2". Alpha 1-antitrypsin is the main protein of the alpha-globulin 1 region.
Another name used is alpha-1 proteinase inhibitor (α1-PI).
Read more about this topic: Alpha 1-antitrypsin