Serum-free and reduced serum formulations often require purified forms of the factors normally supplied by serum that are suitable for in vitro growth and differentiation studies. These important factors include insulin, transferrin, selenium, pyruvate, and ethanolamine.

INSULIN is a polypeptide hormone that promotes the uptake of glucose and amino acids and may owe observed mitogenic effect to this property.

TRANSFERRIN is an iron-transport protein. Iron is an essential trace element, but can be toxic in the free form. To nourish cells in culture, it is supplied bound to transferrin in serum.

SELENIUM is an essential trace element normally provided by Serum.

Nutritional studies indicate that the supplement components described are utilized by most mammalian cells. They enhance cell proliferation and decrease the serum requirement of many cell types. When the provided supplement is used with 2 to 4 percent serum, proliferation is reported to be similar to medium supplemented with 10 percent serum.