ABSTRACT
The major function of γ-glutamyltransferase is related to the interorgan metabolism of glutathione. Suggestions have been made that the glutaminase reaction would contribute significantly to the catalysis by γ-glutamyltransferase in vivo. γ-Glutamyltransferase is a plasma membrane bound enzyme exposed on the outside of cells primarily involved in secretion and absorption. The measurements of γ-glutamyltransferase in serum have been of considerable interest in diagnostic enzymology, as increased serum activity is a sensitive indication of liver disease. "Novel forms" of the enzyme have been described in neoplastic tissues, but these variants are not true isoenzymes, as they show identical antigenic properties to the enzymes in nonneoplastic tissue. The intraorgan metabolism of glutathione is also initiated by the efflux of glutathione. The kidney cells are excreting significant amounts of glutathione into the tubular lumen, which is then effectively degraded and reabsorbed as free amino acids.
