Extracellular glutathione is a source of cysteine for cells that express gamma-glutamyl transpeptidase.
We show that gamma-glutamyl transpeptidase (GGT) is a glutathionase that enables cells to use extracellular glutathione as a source of cysteine. We transfected NIH/3T3 mouse fibroblasts with a plasmid containing cDNA for human GGT, and obtained stably transformed cell lines that expressed GGT in its proper orientation on the outer surface of the cell. NIH/3T3 fibroblasts require cysteine for growth and are unable to use extracellular glutathione as a source of cysteine. We demonstrate GGT-positive fibroblasts are able to grow in cysteine-free medium supplemented with glutathione. Cysteine derived from the cleavage of extracellular glutathione can be used to maintain intracellular levels of glutathione. GGT-positive NIH/3T3 cells were able to replenish intracellular glutathione when incubated in cysteine-free medium containing glutathione. GGT-negative cells could not. Therefore, GGT is a glutathionase that provides the cell with access to a secondary source of cysteine.
Hanigan
M H
MH
Department of Anatomy and Cell Biology, School of Medicine, University of Virginia, Charlottesville 22908.
Ricketts
W A
WA
D016475:3T3 Cells; D000818:Animals; D003470:Culture Media; D003545:Cysteine / Q000378:metabolism*; D004247:DNA; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000201:enzymology; D051379:Mice; D051381:Rats; D005723:gamma-Glutamyltransferase / Q000096:biosynthesis* / Q000235:genetics
D003470:Culture Media; D004247:DNA; D005723:gamma-Glutamyltransferase; D005978:Glutathione; D003545:Cysteine