Neurophysin I is a carrier protein with a size of 10 K Da and contains 90 to 97

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s. It is a cleavage product (formed by splitting of a compound molecule into a simpler one) of preprooxyphysin. It is a neurohypophysial

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

that is transported in vesicles with

oxytocin Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include Human bonding, ...

, the other cleavage product, along

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s, from magnocellular neurons of the

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

to the posterior lobe of the pituitary. Although it is stored in neurosecretory granules with oxytocin and released with oxytocin, its biological action is unclear.

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 Mammalian vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the ''AVP'' gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It ...

, a hormone similar in structure to oxytocin, is analogously bound and transported by

Neurophysin II Neurophysin II is a carrier protein with a size of 19,687.3 Da and is made up of a dimer of two virtually identical chains of amino acids. Neurophysin II is a cleavage product (formed by splitting of a compound molecule into a simpler one) of ...

. 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

{{Oxytocin and vasopressin receptor modulators Integral membrane proteins

Function

Structure

See also

References