Cell cycle changes in transformed cells growing under serum-free conditions.

Polyoma transformed hamster cells (PyBHK) and SV40 transformed mouse cells (SV3T3) were transferred in culture using crystalline trypsin followed by neutralisation with soybean trypsin inhibitor. Such cells were able to proliferate freely in defined medium without any serum supplement and without any intervening period of adaptation. However, growth rates were reduced under serum-free conditions. Re-establishment of rapid growth rates could be achieved by addition of serum, with the rate attained being proportional to the serum concentration. Irrespective of the prevailing rates of growth, percentages of cells synthesising DNA were the same. However, the rate at which DNA was being synthesised was found to change proportionately with the changes in overall growth rate.