The nutrient requirements of MRC-5 human diploid cells.

Nutrients were assayed by their effect on maximum cell yield (maximum cell population less inoculum) of MRC-5 cells previously maintained in Eagle's basal medium with 10% (v/v) serum, trypsinised, centrifuged and washed. When nonlimiting amounts of iron, methylcellulose and a 68-component supplement were included in our defined medium, cell yields obtained were equivalent to those obtained with 2 to 3% whole serum. Growth then became limited by serum growth factors which, when serum was fractionated by the low temperature ethanol procedure, appeared to precipitate with the alpha-globulins, although the distribution of activity varied from batch to batch of serum. Column chromatography (DEAE and concanavalin A-Sepharose) of serum resulted in much (20 to 45%) loss of growth factor activity during exhaustive dialysis or Sephadex G-25 desalting suggesting that the growth factor may be a diffusible molecule bound in serum to a large protein carrier.