Modes of Mediated Exodus of Amino Acids from the Ehrlich Ascites Tumor Cell

Conditions have been described for the observation of the efflux of amino acids from the Ehrlich cell as a function of concentration. Failure to use very large volumes of suspending medium gives rise to confusion between factors influencing exodus and those affecting re-entry. The neutral and cationic amino acids that enter this cell by specific mediated transport show net exodus from the cell by routes with patterns of analogue inhibition similar to those for their entry. Two model amino acids whose entry is specific each to a different mediating system do not show significant interaction for exodus. Phenylalanine escapes partly by a route inhibitable by one of these models, partly by a route inhibitable by the other. Alanine exodus appears to divide itself among the systems serving principally for its entry, although in somewhat different proportions. The competition for entry shown between lysine and substrates of the L system is also seen for exodus, with indications that a portion of the exodus of lysine escapes that inhibition, as is the case for entry. The apparent Km values for exodus are in general much higher than those for entry, whereas the Vmax values for the two directions are similar. A component of exodus of neutral α-amino acids with a relative rate of slightly less than 0.03 min−1 appears not to be subject to saturation, in correspondence to the magnitude of a similar component of entry. Little or no reactivity for alanine exodus by countertransport has been found except by one of two Na+-dependent systems.