Process for separating α1-proteinase inhibitor from cohn fraction IV1 and IV4 paste

A process for purifying α1-proteinase inhibitor comprising:

• providing an impure protein fraction comprising α1-proteinase inhibitor;
• suspending the impure protein fraction comprising α1-proteinase inhibitor in water;
• precipitating the impure protein fraction comprising α1-proteinase inhibitor with a precipitant comprising polyethylene glycol (PEG) and ZnCl2;
• collecting the supernatant from the PEG/ZnCl2 precipitation, wherein the supernatant comprises α1-proteinase inhibitor;
• precipitating α1-proteinase inhibitor from the PEG/ZnCl2 supernatant with ZnCl2 at a concentration of 5 to 15 mM to thereby provide an α1-proteinase inhibitor precipitate;
• resuspending the α1-proteinase inhibitor precipitate in an aqueous medium;
• applying the resuspended α1-proteinase inhibitor to an anion-exchange chromatography medium;
• applying α1-proteinase inhibitor recovered from the anion-exchange chromatography medium to a metal chelate medium;
• and
• recovering a fraction comprising α1-proteinase inhibitor from the metal chelate medium.