Method for preventing reduction of polypeptide by adding amino acid to culture solution

1. A method for purifying a polypeptide from a culture solution containing the polypeptide and a recombinant host cell which is capable of producing the polypeptide, said method comprising the following steps:

(a) a flocculation step, wherein the flocculation step comprises acid precipitation of the culture solution;

(b) centrifuging the culture solution of step (a) to recover a culture supernatant;

(c) filtering the culture supernatant; and

(d) isolating the polypeptide from the filtrate obtained from step (c),

wherein the method further comprises adding arginine to the culture solution either before or after step (a).

2. The method according to claim 1 , wherein the polypeptide is an antibody or an antibody fragment.

3. The method according to claim 1 , wherein the recombinant host cells are Chinese hamster ovary (CHO) cells.

4. The method according to claim 1 , wherein the arginine is added to the culture solution before step (a).

5. The method according to claim 1 , wherein the arginine is added to the culture solution after step (a).

6. The method according to claim 5 , wherein the arginine is added to the culture solution so that the final concentration of the arginine is from 0.05 mol/L to 1 mol/L.

7. The method according to claim 5 , wherein the arginine is added to the culture solution so that the final concentration of the arginine is 0.5 mol/L.

8. The method according to claim 5 , wherein the arginine is added to the culture solution so that the final concentration of the arginine is 0.1 mol/L.

9. The method according to claim 5 , further comprising adding arginine to the culture solution after step (c).

10. The method according to claim 5 , wherein arginine is added to the culture solution after step (a), and before step (b).