*2.1. Cell Culture*

HeLa cells (derived from human cervical cancer) were grown in DMEM supplemented with 10% fetal bovine serum and antibiotics (100 U/mL penicillin and 100 μg/mL streptomycin). According to the formulation for DMEM it does not contain vitamin C. Vitamin C was not detectable in the batch of serum used. Cells were maintained as monolayer cultures at 37 °C in a humidified atmosphere with 5% CO2 and routinely passaged by trypsinization when nearly confluent.
