Gamma-glutamyl transpeptidase-mediated transport of amino acid in lecithin vesicles.

Gamma-Glutamyl transpeptidase, a membrane-bound enzyme purified from hog kidney cortex following solubilization with detergent, was incorporated by sonication procedure into large phospholipid vesicles using a 1:2 molar ratio of deoxycholate to phospholipid. tthese vesicles, when containing entrapped glutathione, exhibited the uptake of L-[14C]glutamate, but not of L-proline. The glutamate uptake did not occur to a significant extent in these vesicles when glutathione was added externally. The uptake of glutamate in the reconstituted system was sensitive to the temperature of incubation and to the inhibitors (serine-borate, azaserine, and 6-diazo-5-oxo-L-norleucine) of gamma-glutamyl transpeptidase activity. The accumulated product during the transport of glutamate in the gamma-glutamyl transpeptidase reconstituted system containing intravesicular glutathione was identified as gamma-glutamyl-glutamate. These results indicate that gamma-glutamyl transpeptidase mediates the translocation of glutamate in vitro and provides evidence in support of its role in the transport of amino acids in natural membranes.