Transport of Diamino Acids into the Ehrlich Cell

From the ¹ From the Department of Biological Chemistry, The University of Michigan, Ann Arbor, Michigan 48104

The mediated uptake of lysine by the Ehrlich cell shows a heterogeneity in its accessibility to inhibition by other amino acids: a portion of about 60% that can be eliminated by the presence of phenylalanine in excess; a minor portion that can be eliminated by various neutral amino acids, although not by phenylalanine; and another minor saturable portion that cannot be inhibited by neutral amino acids. The latter component shows a doubling of its rate on the removal of the sodium ion from the medium. The described heterogeneity of lysine transport might be explained in either of two ways. First, one might propose three independent transport-mediating systems for lysine, none of them identical with any serving for the neutral amino acids. Alternatively, the leucine-preferring and lysine-preferring receptor sites may lie on a common transport-mediating system, the phenomena of partial inhibition of lysine transport by neutral amino acids and of neutral amino acid transport by lysine arising from the handicap that filling of one of the sites presents to the operation of the other. A parallelism in the loss of countertransport by leucine and lysine on treatment with dinitrofluorobenzene indicates at least a common feature if not a common step for two of the processes concerned.

The entry of -N-methyl-l-lysine, which was unreactive with the above transport agencies, showed a first order rate constant of 0.003 min^-1, providing a maximal value for entry by simple diffusion.

At least two of these three components contribute to the uptake of ,-diaminobutyric acid, but its intense uptake at high concentration (and that of its lower homologue) is produced by an atypical use of the usual alanine-preferring (A) system. Possible bases for that atypical operation of the A system are discussed.

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