GGCT Full-Length MS Protein Standard (NP_076956), Labeled with [U- 13C6, 15N4]-L-Arginine and [U- 13C6, 15N2]-L-Lysine, was produced in human 293 cells (HEK293) with fully chemically defined cell culture medium to obtain incorporation efficiency at Creative-Proteomics. The protein encoded by this gene catalyzes the formation of 5-oxoproline from gamma-glutamyl dipeptides, the penultimate step in glutathione catabolism, and may play a critical role in glutathione homeostasis. The encoded protein may also play a role in cell proliferation, and the expression of this gene is a potential marker for cancer. Pseudogenes of this gene are located on the long arm of chromosome 5 and the short arm of chromosomes 2 and 20. Alternatively spliced transcript variants encoding multiple isoforms have been observed for this gene.