Glutamine: a major energy source for cultured mammalian cells.

Cultured mammalian cells have two primary mechanisms for obtaining energy necessary for growth: carbohydrate metabolism to lactate and glutamine oxidation to CO2. In tissue culture medium containing both glucose and glutamine, the contribution of glutamine oxidation to the energy requirement ranges between 30 and 50%. As the glucose concentration is decreased, or when glucose is replaced by other carbohydrates, the rate of glutamine oxidation increases and glutamine becomes the sole energy source for cultured cells. The rate of glutamine oxidation is regulated by the presence of glucose. The apparent absolute requirement for glucose or other carbohydrates in tissue culture medium is related to its role in anabolic reactions rather than in energy production. Oxidation of glucose, fatty acids, or ketone bodies does not contribute significantly to the energy needs of cultured mammalian cells. The data also suggest that consideration should be given to glutamine as an important energy source in vivo.