GGT1 and diabetes mellitus: As we recently proposed [16] that the increased levels of ANPEP mRNA in pancreatic beta cells and plasma levels of GGT1 (gamma-glutamyltransferase) in T2D patients may be indicative of an adaptive mechanism in response to endogenous glutathione deficiency: up-regulation of these membrane-bound enzymes in diabetes is necessary for the sequential production of three amino acids (AA)—precursors for intracellular GSH biosynthesis.