Epsilon-(gamma-glutamyl)-lysine

Epsilon-(gamma-glutamyl)-lysine (H-Glu (H-Lys-OH)-OH) is specifically cleaved in the presence of γ-glutamyl cyclotransferase (25 μg/mL) at 37°C for 3 h. The radiolabeled heterodipeptide peak almost completely disappears, while a lysine peak appears, indicating that Epsilon-(gamma-glutamyl)-lysine is a substrate of this enzyme^[1].
When exogenously radiolabeled ε-(γ-glutamyl)-lysine is added to pre-fusion CHO cells (24 h), it can be fully recovered in the unmodified form of Nε-(γ-glutamyl)-lysine, indicating that this heterodipeptide is not taken up by CHO cells nor modified in the culture medium^[1].
The content of ε-(γ-glutamyl)-lysine in the free protein fraction reaches 188-238 pmol/10⁷ cells, and that in the culture medium reaches 35-48 pmol/mL when CHO cells are cultured for 48 h. Its content increases with the rise of cell density, peaking at 460 pmol/10⁷ cells in the free protein fraction and 61 pmol/mL in the culture medium respectively when cells are confluent^[1].
The formation of ε-(gamma-glutamyl)-lysine in CHO cells and culture medium is inhibited by intracellular protein degradation inhibitors; Methylamine (20 mM) almost completely prevents its occurrence, Leupeptin (HY-18234) (0.2 mM) also exerts a significant inhibitory effect, while Chymostatin (HY-P3042) (0.2 mM) shows a weaker effect. Meanwhile, protein-bound Nε-(γ-glutamyl)-lysine increases, which supports that the free heterodipeptide originates from proteolytic degradation of cross-linked proteins^[1].
Epsilon-(gamma-glutamyl)-lysine exists as protein cross-links in renal tissues of human diabetic nephropathy (DN). Its immunofluorescence intensity increases from 3.02 mV/μm² in normal renal tissues to 14.68 mV/μm² in DN renal tissues. It mainly distributes in the extracellular regions around glomeruli and renal tubules, and correlates with the degree of renal scarring and the estimated glomerular filtration rate^[2].
Epsilon-(gamma-glutamyl)-lysine exists in the form of protein cross-links in all examined scar tissues of failed filtering blebs after glaucoma filtering surgery. Its staining is most prominent at the edge of the Tenon's capsule and shows almost complete colocalization with fibronectin, suggesting that it can reflect tissue transglutaminase-mediated extracellular matrix cross-linking^[3].
Epsilon-(gamma-glutamyl)-lysine cross-links show weak staining in the untreated incision area of the ex vivo trabeculectomy model using human donor eyes^[3].

MedChemExpress (MCE) has not independently confirmed the accuracy of these methods. They are for reference only.