 Each is a peptide of nine amino acids derived from a preprohormone precursor by proteolytic cleavage, with an intramolecular disulfide bridge between the cysteine (Cys) residues; the C-terminal glycine (Gly) residue is amidated.Six of the residues have been found to be invariant in homologous peptides from numerous species of vertebrates.The vasopressin-like peptides, which differ in positions 3 and/or 8, include AVT and the mammalian hormones arginine vasopressin (Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2, with isoleucine-3 of AVT changed to phenylalanine) and lysine vasopressin (isoleucine-3 changed to phenylalanine and arginine-8 changed to lysine).