Extraction from cheese whey by cation-exchange chromatography of factors that stimulate the growth of mammalian cells

Bovine cheese whey was investigated as a source of growth-stimulating factors that might replace or supplement fetal bovine serum in cell culture. Although some cell growth activity was demonstrated in whey or whey ultrafiltrates, enrichment on the basis of molecular size was not useful because the most abundant whey proteins, beta-lactoglobulin and alpha-lactalbumin, have molecular masses that are similar to most known growth factors. Instead, cation-exchange chromatography was selected as an enrichment process because, in contrast to the major whey proteins, growth factors generally have basic isoelectric points. Adsorption to and elution from Sepharose Fast Flow-S resin yielded an extract containing only 1 to 2% of whey protein but substantial growth-promoting activities on Balb/c 3T3 cells, L6 myoblasts, and human skin fibroblasts. The growth activity could be separated from lactoferrin, one of the prominent basic proteins present, through a stepwise elution from the resin. The resultant fraction, which contained lactoperoxidase as the most abundant protein stimulated the growth of the three cell lines at protein concentrations that were 2- to 20-fold lower than observed with fetal bovine serum. Immunoglobulin G could be removed by affinity chromatography, or lactoperoxidase could be inactivated by heat, without significant losses to the growth-promoting capacity of the fraction. These results suggest that enrichment of growth factors by cation-exchange chromatography offers a practical method for the large-scale isolation of an extract from cheese whey that stimulates cell growth.