Structure and Relation To Oxytocin
The vasopressins are peptides consisting of nine amino acids (nonapeptides). (NB: the value in the table above of 164 amino acids is that obtained before the hormone is activated by cleavage). The amino acid sequence of arginine vasopressin is Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly, with the cysteine residues forming a disulfide bond. Lysine vasopressin has a lysine in place of the arginine.
The structure of oxytocin is very similar to that of the vasopressins: It is also a nonapeptide with a disulfide bridge and its amino acid sequence differs at only two positions (see table below). The two genes are located on the same chromosome separated by a relatively small distance of less than 15,000 bases in most species. The magnocellular neurons that make vasopressin are adjacent to magnocellular neurons that make oxytocin, and are similar in many respects. The similarity of the two peptides can cause some cross-reactions: oxytocin has a slight antidiuretic function, and high levels of AVP can cause uterine contractions.
Below is a table showing the superfamily of vasopressin and oxytocin neuropeptides:
| Vertebrate Vasopressin Family | ||
|---|---|---|
| Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2 | Argipressin (AVP, ADH) | Most mammals |
| Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Lys-Gly-NH2 | Lypressin (LVP) | Pigs, hippos, warthogs, some marsupials |
| Cys-Phe-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2 | Phenypressin | Some marsupials |
| Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Arg-Gly-NH2 | Vasotocin† | Non-mammals |
| Vertebrate Oxytocin Family | ||
| Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 | Oxytocin (OXT) | Most mammals, ratfish |
| Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Pro-Gly-NH2 | Prol-Oxytocin | Some New World monkeys, northern tree shrews |
| Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Ile-Gly-NH2 | Mesotocin | Most marsupials, all birds, reptiles, amphibians, lungfishes, coelacanths |
| Cys-Tyr-Ile-Gln-Ser-Cys-Pro-Ile-Gly-NH2 | Seritocin | Frogs |
| Cys-Tyr-Ile-Ser-Asn-Cys-Pro-Ile-Gly-NH2 | Isotocin | Bony fishes |
| Cys-Tyr-Ile-Ser-Asn-Cys-Pro-Gln-Gly-NH2 | Glumitocin | Skates |
| Cys-Tyr-Ile-Asn/Gln-Asn-Cys-Pro-Leu/Val-Gly-NH2 | Various tocins | Sharks |
| Invertebrate VP/OT Superfamily | ||
| Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-Gly-NH2 | Diuretic Hormone | Locust |
| Cys-Phe-Val-Arg-Asn-Cys-Pro-Thr-Gly-NH2 | Annetocin | Earthworm |
| Cys-Phe-Ile-Arg-Asn-Cys-Pro-Lys-Gly-NH2 | Lys-Connopressin | Geography & imperial cone snail, pond snail, sea hare, leech |
| Cys-Ile-Ile-Arg-Asn-Cys-Pro-Arg-Gly-NH2 | Arg-Connopressin | Striped cone snail |
| Cys-Tyr-Phe-Arg-Asn-Cys-Pro-Ile-Gly-NH2 | Cephalotocin | Octopus |
| Cys-Phe-Trp-Thr-Ser-Cys-Pro-Ile-Gly-NH2 | Octopressin | Octopus |
| †Vasotocin is the evolutionary progenitor of all the vertebrate neurohypophysial hormones. | ||
Read more about this topic: Vasopressin
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