α-1 antitrypsin is
1. an antacid                           
2. an enzyme
3. used to treat arthritis       
4. used to treat emphysema

(4) α-antitrypsin is a protease inhibitor that is produced by the introduction of specific sequence of DNA (or genes) which codes for a particular product in the transgenic animals. It is used to treat emphysema as it inhibits the enzymes of inflammatory cells that contributes to the respiratory complications.