Neurophysin I

Neurophysin I is a carrier is_associated_with::protein with a size of 10 KDa and containing 90 to 97 is_associated_with::aminoacids that is a cleavage product (formed by splitting of a compound molecule into a simpler one) of preprooxyphysin. It is a neurohypophysial is_associated_with::hormone that is transported in vesicles with is_associated_with::oxytocin, the other cleavage product, along is_associated_with::axons, from magnocellular neurons of the is_associated_with::hypothalamus to the posterior lobe of the is_associated_with::pituitary. Although it is stored in secretory vesicles with oxytocin and released with oxytocin, its biological action is unclear.

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)

Function
Neurophysins are carrier proteins for oxytocin and vasopressin (ADH). Oxytocin and vasopressin are carried by unique neurophysins from their site of production in the cell bodies of the paraventricular and supraoptic nuclei to their site of release in the axon terminals of the posterior pituitary.