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[Production of gastric-mucosa protective collagen Ⅲ by Pichia pastoris].

To improve collagen production by recombinant Pichia pastoris, we applied Placket-Burman and Box-Behnken design to optimize the fermentation medium. Through Placket-Burman design, three variables in the medium (concentration of yeast extract, peptone and glycerol) were selected for having significant effect on cell dry weight. Through Box-Behnken design regression coefficients analysis, a secondary degree polynomial equation was established, and the optimum levels of the three variables were yeast extract 1.13%, peptone 1.61% and glycerol 0.86%. During the growth period, an average cell dry weight of 4.41 g/L was obtained after 12 h fermentation, increased by 26%. Through high density fermentation, the production of recombinant human collagen (Ⅲ) was up to 4.71 g/L in 22 L fermentor. The recombinant human collagen (Ⅲ) exhibited good results to repair acetic acid induced gastric ulcer in rats.