High quality (glyco)proteins are needed for biopharmaceutical applications. They are generally expressed as recombinant proteins in bacteria, yeast, plant and/or animal cells in culture. Growth media are increasingly supplemented with peptones to improve either the cell growth or protein expression or both. To further enhance protein production, it is important to understand the effects of peptones at the cellular and molecular levels. Upon addition of a soy peptone to a cultivation medium of CHO cells, an increased specific productivity was observed. This work aimed at elucidating which main cellular functions are affected by the presence of the peptone. Therefore, hypotheses about putative effects on recombinant protein production steps have been postulated and tested. Although the effects emerge to be multiple, it was found that the peptone increased overall protein translation and recombinant protein secretion. Nonetheless, when other cellular functions (e.g. transcription, glycosylation, proteolytic degradation) were examined, no specific effects were observed. Further experiments are needed to probe the mechanisms related to the influence of the soy peptone on these cellular functions. (C) 2011 Elsevier Ltd. All rights reserved.