Neurophysin I

Function

Neurophysin I is the carrier protein for oxytocin. It is produced in the cell bodies of the paraventricular and supraoptic nuclei and transported to its site of release in the axon terminals of the posterior pituitary. Neurophysin I neurons are more prevalent in the paraventricular nuclei while Neurophysin II neurons are more prevalent in the supraoptic nuclei. Vasopressin, a hormone similar in structure to oxytocin, is analogously bound and transported by Neurophysin II. Both hormones are nine residues long, and share seven of these residues. Oxytocin possesses Ile-3 and Leu-8 whereas vasopressin possesses Phe-3 and Arg-8. Both Ile and Phe are hydrophobic amino acids and undergo analogous binding to neurophysins.

Structure

The amino acid sequence of Neurophysin I is:

NH2 - Ala - Ala - Pro - Asp - Leu - Asp - Val - Arg - Lys - Cys - Leu - Pro - Cys - Gly - Pro - Gly - Gly - Lys - Gly - Arg - Cys - Phe - Gly - Pro - Asn - Ile - Cys - Cys - Ala - Glu - Glu - Leu - Gly - Cys - Phe - Val - Gly - Thr - Ala - Glu - Ala - Leu - Arg - Cys - Gln - Glu - Glu - Asn - Tyr - Leu - Pro - Ser - Pro - Cys - Gln - Ser - Gly - Gln - Lys - Ala - Cys - Gly - Ser - Gly - Gly - Arg - Cys - Ala - Val - Leu - Gly - Leu - Cys - Cys - Ser - Pro - Asp - Gly - Cys - His - Ala - Asp - Pro - Ala - Cys - Asp - Ala - Glu - Ala - Thr - Phe - Ser - Gln – Arg - OH

(Disulfide bridge: 10-54; 13-27; 21-44; 28-34; 61-73; 67-85; 74-79)

References

References

1. (1992). "The human gene for oxytocin-neurophysin I (OXT) is physically mapped to chromosome 20p13 by in situ hybridization". Cytogenet. Cell Genet..
2. (1972). "Demonstration of neurophysin in the hypothalamo-neurohypophysial system of the normal and dehydrated rat by the use of cross-species reactive anti-neurophysins.". Zeitschrift für Zellforschung und mikroskopische Anatomie.