Neurophysin

Neurophysin is a type of protein that is involved in the storage and release of neuropeptides in the neuroendocrine system. It is a carrier protein, which means it binds to specific neuropeptides and transports them to their destination. Neurophysin is particularly associated with the neuropeptides oxytocin and vasopressin, which are important for a variety of physiological functions.

Structure

Neurophysin is a relatively small protein, with a molecular weight of approximately 10,000 daltons. It is composed of a single polypeptide chain, which is folded into a compact, globular shape. The structure of neurophysin is stabilized by several disulfide bonds, which form between specific cysteine residues in the protein.

Function

The primary function of neurophysin is to bind to and transport neuropeptides. It is synthesized in the neurons of the hypothalamus, along with the neuropeptides it carries. Once synthesized, neurophysin and its associated neuropeptide are packaged into vesicles for transport down the axon of the neuron. When the neuron is stimulated, these vesicles fuse with the cell membrane and release their contents into the bloodstream.

Neurophysin has a high affinity for its associated neuropeptides, which ensures that the neuropeptides are efficiently transported and released. However, once in the bloodstream, the neuropeptides dissociate from neurophysin and bind to their specific receptors on target cells.

Clinical significance

Mutations in the genes that encode for neurophysin can lead to a variety of disorders. For example, mutations in the gene for neurophysin II, which carries vasopressin, can cause diabetes insipidus, a condition characterized by excessive thirst and urination. Similarly, mutations in the gene for neurophysin I, which carries oxytocin, can lead to problems with childbirth and lactation.

See also

• Neuropeptide
• Oxytocin
• Vasopressin
• Diabetes insipidus