The biotin requirement of HeLa cells.

We have examined the effect of alterations in the biotin content of the medium on the growth, viability, biotin content, and the activities of biotin-independent and biotin-independent enzymes of the HeLa cells. The inclusion in the growth medium of avidin, which almost irreversibly binds with biotin (Kd, 10(-15) M), results in an increase in cellular biotin content and biotin enzyme activity over that seen when the cells are grown in a biotin-depleted medium. The addition of avidin-bound biotin to the growth medium led to a forty-fold increase in cellular biotin when compared to the inclusion of an equivalent amount of free biotin in the medium. HeLa cells are able to internalize avidin-bound biotin. Biotin is released from this complex to function as the prosthetic group of biotin enzymes. HeLa cells do have a nutritional requirement for biotin.