Effects of serum on membrane transport. III. Serum and inhibition of lysine transport.

Rabbit lung macrophages have been shown to transport lysine by means of a single carrier-mediated system that is depressed after relatively short incubations with 1% normal rabbit serum (NRS). Our present results show that three amino acids, glutamine, phenylalanine and tyrosine, at or near the concentration found in 1% NRS, are involved intracellularly in regulating lysine influx across the plasma membrane. The means by which they do so requires a 20- to 30-min preincubation, the effect is maintained for 45 min in their absence, and both maximal velocity and affinity of lysine for its carrier are altered in an apparently uncompetitive fashion. The kinetic data are unlike those reported for other trans phenomena involved in amino acid transport. We propose that the effect of internal inhibitor on lysine influx probably does not involve the direct interaction of the transamino acid on the lysine carrier.