초록
The effects of pH on recombinant human erythropoietin (rHuEPO) production by Pichia pastoris was investigated at pH=4.0, 4.5, 5.0, 5.5 and 6.0, where sorbitol and methanol were supplied to the bioreactor in batch and fed-batch mode, respectively, in the recombinant protein production phase (PP). For the first three phases, glycerol batch (GB), glycerol fed-batch (GFB) and methanol transition (MT), the growth profiles were almost the same for pH>=5.0; however, at pH<5.0 the growth rate was lower. The highest cell concentration was obtained as 81.4gL<SUP>-1</SUP> where GB and GFB were operated at pH=5.0 and MT and PP were operated at pH=4.5. Sorbitol added at the beginning of PP, was totally consumed within 15h, at pH@?5.0; however, at pH>5.0 sorbitol consumption rate decreased. The highest rHuEPO concentration was achieved at pH=4.5 as 0.16gL<SUP>-1</SUP>, where the overall cell and rHuEPO yield on substrate, were 0.5gg<SUP>-1</SUP> and 1.5mgg<SUP>-1</SUP>. pH did not have a significant effect on extracellular protease activity. The highest specific AOX activity (110Ug<SUP>-1</SUP> CDW) was attained at pH=4.5 parallel to the highest rHuEPO production. At pH=4.5, higher oxygen demand of the cells resulted in higher oxygen K<SUB>L</SUB>a, 0.11s<SUP>-1</SUP>, values.