The metabolism of L‐glutamate and L‐5‐Carboxypyrrolidone by mouse cells (NCTC clone 929) under conditions of defined nutrition

Abstract

The utilization of L-glutamate by clone 929 mouse cells growing in a synthetic medium, MAL 294/2, was studied with the aid of carbon-14 labeled L-glutamate. The rate of consumption of extracellular glutamate was rapid even though the extracellular concentration of this substance has been found to remain constant or to increase. The rate of uptake during an interval of otpimal growth was calculated to be approximately 42 mpmoles/mg of cell protein per hour.Among the metabolic products that are derived from the carbon of glutamate and secreted from the cells are carbon dioxide, lactic acid, proline, alanine, alpha-ketoglutaric acid and 5-carboxypyrrolidone. Aspartic acid, although produced by the cells in amounts sufficient to meet the needs for growth, does not appear as an extracellular product of glutamate metabolism. Extracts of L cells were found to exhibit four times as much glutamic-oxaloacetic as glutamic-pyruvic transaminase activities. Failure to secrete aspartic acid must not be due to a deficiency in the transaminase. The transaminase concentrations are apparently not affected by variations in the concentrations of aspartic acid and alanine in the medium, both of which are absent from MAL 294/2. 5-Carboxypyrrolidone, although produced from L-glutamate by L cells, is metabolically inert in this system. Likewise, mouse fetal lung cells, cultured in a similar way, use glutamic acid as extensively as L cells and fail to metabolize exogenous 5-carboxypyrrolidone.

Synthesis of proline and hydroxyproline in human lung (WI-38) fibroblasts

“…Glutamate is not a good substitute for glutamine in the nutrition of cultured cells (Levintow & Eagle, 1961), but is nevertheless metabolized by a variety of cells (Levintow et a!., 1957;Salzman et al, 1958;Kitos & Waymouth, 1966) including WI-38 fibroblasts (Griffiths, 1970). These experiments provided further substantiation for the relatively rapid consumption ofglutamate.…”