γ-glutamyltransferase in human diploid fibroblasts and other mammalian cells

Summary γ-Glutamyltransferase was determined in WI-38 human diploid fibroblasts and compared to enzyme levels determined in several other mammalian cell lines including: fibroblast-like cells from human skin, tibia and foreskin; epithelial-like cells from human, bovine and monkey kidney; and transformed cells (Chinese hamster ovary, HeLa S₃ and SV-40 transformed WI-38). Transformed cells had the lowest activity found followed in increasing order by fibroblasts, human and bovine epithelial cells and monkey kidney epithelial cells. The enzyme isolated from the plasma membrane of WI-38 cells, like the enzyme from kidney and brain, was found to be irreversibly inhibited by iodoacetamide, reversibly by serine-borate, and had a strong specificity for certain amino acids. The possibility exists that γ-glutamyltransferase could be involved in transport of amino acids into cells in culture; and glutamine, used in media, is an excellent substrate for the enzyme. Preliminary reports of some of this work were presented at meetings of The American Society of Biological Chemists in Minneapolis (Abstracts Fed. Proc. 33: 957, 1974) and at Atlantic City (Abstracts Fed. Proc. 34: 2243, 1975). This work was supported by Grant NIH 1 P01 HD 07173. The WI-38 starter cultures and cell pack used in these studies were obtained through Contract M01 HD 42828 to Stanford University from the National Institute of Aging.