Tumors function as a
nitrogen trap, and they compete with the host for
nitrogen compounds. In experiments with whole animals infected with Ehrlich ascitic
tumor cells, the
glutamine,
glutamate,
asparagine, and
aspartate concentrations were determined for host plasma, ascitic liquid, and
tumor cells, throughout the period of
tumor growth. Concentration gradients of
glutamine or
asparagine were created from the host tissues towards the ascitic liquid. The countergradient step from ascitic liquid to
tumor cells may be overcome by an active transport process with an apparent Km for
glutamine of 3.1 X 10(-4) M. On the other hand, a reverse flux of
glutamate and
aspartate was seen to take place from cells to plasma. In vitro incubations of
tumor cells with near physiological concentrations of
glutamine, or
asparagine plus
glucose, confirmed the host-to-
tumor nitrogen movement previously deduced from the relative
amino acid concentrations in plasma, ascitic liquid, and
tumor cells. The ammonemia detected in
tumor-bearing mice at the terminal stage could result from the hydrolysis of
glutamine, which was rapidly metabolized by the
tumor cells.