MEM α is a modification of Minimum Essential Medium (MEM) that contains non-essential amino acids, sodium pyruvate, lipoic acid, vitamin B12, biotin, and ascorbic acid. MEM α is available without nucleosides for use as a selection medium for DG44 and other DHFR-negative cells. This product is made with Earle’s salts. MEM α contains no proteins, lipids, or growth factors. Therefore, MEM α requires supplementation, commonly with 10%Fetal Bovine Serum(FBS). MEM α uses a sodium bicarbonate buffer system (2.2 g/L), and therefore requires a 5–10% CO2environment to maintain physiological pH.