In conclusion, this analysis has identified the spectrum of peptidesproduced by human and mouse islets in health and metabolic disease,including post-translational modifications and exact peptide sequences.While we could detect active GLP-1 in both human and mouse islets,levels were 100–1000 fold lower than glucagon, suggesting thatthe activity of glucagon on beta cell GLP1R would overcome any effectof local GLP-1 production. Here, GCG is linked to metabolic disease.