Histidine transport in plasma membrane vesicles from rat liver.

The transport of L-histidine, a selective substrate for system N, across liver plasma membrane vesicles has been studied. The amino acid is accumulated sevenfold within the intravesicular space in the presence of a sodium gradient. Lithium can replace sodium to some extent in the cotransport mechanism. The amino acid translocation is not influenced by the transmembrane electrical potential difference. Histidine kinetics involves a saturable component plus a linear one both in the presence and in the absence of sodium. Sodium affects mainly the affinity of the translocator and to a lesser extent its mobility. Histidine uptake is competitively inhibited by glutamine and it is affected by alanine in a noncompetitive manner.