Glycosylation patterns and specific expression rates of the recombinant protein mouse placental lactogen-I (mPL-I) by Chinese hamster ovary (CHO) cells varied significantly over the extracellular pH (pHe) range of 6.1 to 8.7. The maximum specific mPL-I expression rates occurred between pHe 7.6 and 8.0. The pHe effect on protein expression was confirmed using a different CHO cell expressing the unglycosylated recombinant protein mouse placental lactogen-II (mPL-II). Decreases in the extent of glycosylation of mPL-I were observed at low (below 6.9) and high (above 8.2) pHe values. The pHe dependent variations in mPL-I accumulation in the supernatant as well as in glycosylation patterns were not the result of enzymatic degradation in the culture medium.
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