J. Biol. Chem., Vol. 255, Issue 10, 4399-4402, May, 1980
Gamma-glutamyl transpeptidase-mediated transport of amino acid in lecithin vesicles
SC Sikka and VK Kalra
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.
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