A cyclized derivative of l-glutamic acid. Elevated blood levels may be associated with problems of glutamine or glutathione metabolism.

C. difficile Toxin B (392 - 401)

Xenin-8, a C-terminal octapeptide, is a biologically active fragment of Xenin. Xenin is a 25-amino acid peptide of the neurotensin/xenopsin family. Xenin-8 stimulates basal insulin secretion and potentiates the insulin response to glucose in a dose-dependent manner (EC50=0.16 nM).