Oxytocin

What is oxytocin?

Oxytocin (Oxt) is a peptide that has both a hormone and neuropeptide function.

Structure

Oxytocin is a peptide composed of nine amino acids and one non-peptidic substituent. The sequence is as follows:

cysteine-tyrosine-isoleucine-glutamine-asparagine-asparagine-cysteine-proline-leucine-glycine-amide

Cys – Tyr – Ile – Gln – Asn – Cys – Pro – Leu – Gly – NH2

CYIQNCPLG-NH2

XNOPRXBHLZRZKH-DSZYJQQASA-N

3D structure

In its structure at the C-terminal end it is in the form of a primary amide. In addition, the cysteine amino acids form a disulfide bond. It has a molecular mass of 1007 Da. Although the structure of this peptide is conserved in placental mammals. However, changes in this structure have been found in marmosets, tamarins and other primates around the world. Different variants to the sequence have been found. For example, at position 8 the change of the amino acid proline to leucine (Pro8-OT), Ala8-OT, Thr8-OT, Phe2-OT and Val3 / Pro8-OT.

The biologically active form of oxytocin, known as octapeptide (oxytocin disulfide), corresponds to its oxidized form. However, oxytocin also exists as a non-peptide of reduced dithiol straight-chain (non-cyclic) oxytocein.
It is thought that oxytocein may act as a free radical scavenger.

The structure of oxytocin is very similar to that of vasopressin.

Both are non-peptides with a single disulfide bridge, differing only by two substitutions in the amino acid sequence:
Cys – Tyr – Phe – Gln – Asn – Cys – Pro – Arg – Gly – NH2.

Total synthesis

In 1955, Vicent du Vigneaud was awarded the Nobel Prize for the first synthesis of a polypeptide hormone.

A schematic of the total synthesis he performed in 1954 is illustrated in the figure:

 
fig-1