The chemical link that joins amino acids together to form a peptide — and the bond that digestive enzymes break down when you swallow a peptide.Formed between the carboxyl group of one amino acid and the amino group of the next, releasing a water molecule. The backbone of all peptides and proteins. Peptide bonds are hydrolyzed by peptidases (proteases) — which is why oral bioavailability of peptides is near zero. The peptide bond’s vulnerability to hydrolysis is the fundamental pharmacological challenge of peptide drug delivery.