Hormones polypeptide, storage

Thyroxine (T4) and the more potent triiodothyronine (T3) are cleaved from a large precursor protein called thyroglob-ulin. Thyroglobulin exists as a dimer of two identical polypeptides (Mr 330,000). It is a storage protein for iodine and can be considered a prohormone of the circulating thyroid hormones. Thyroglobulin is secreted into the lumen of the thyroid gland, where specific residues are iodinated in... 

Most polypeptides and proteins are water-soluble or water swellable. Enzymes are proteins that catalyze all chemical reactions of biological origin. Enzyme functions include oxygen transport, muscle movement, nerve response, nutrient digestion and storage, hormonal regulation gene expression, and protein synthesis. 

Insulin, Inutral Optisulin long. Polypeptide hormone produced in the beta cells of the islets of Laager-bans situated in the pancreas of all vertebrates. Synthesized in vivo via a single chain polypeptide precursor, proinsulin, native conformation has been established. Secreted directly into the bloodstream where it regulates carbohydrate metabolism, influences the synthesis of protein and of RNA, and the formation and storage of neutral lipids. The first protein for which chemical structure and precise mol wt were determined Sanger, Tuppy, Biochem. J. 49, 463, 481 (1951) ... 

The diverse class of polypeptides allows for the realization of, on the one hand, high-performance construction materials, such as dragline spider silk, microtubules, or collagen fibers. On the other hand, (multi)functional molecules or molecular assemblies can be found, for example, necessary for biocatalysis (enzymes) or for the function of the immune system (immune globulins). Moreover, proteins participate in the storage and the directed transport of materials in biological systems and are essential components for the communication in complex biosystems in form of, for example, cell-surface markers, receptors, regulators, or hormones. 

The role of the pituicyte in the secretory mechanism of the antidiuretic hormone remains unsettled. This cell could act as a storage site for the active polypeptides, which would then be released from the cells of the posterior lobe into the bloodstream as needed. The posterior lobe is more sensitive to changes in the water content of blood because it is not separated from circulating blood by the blood-brain barrier. That the pituicytes affect polypeptide hormone secretion is suggested by the fact that continued stimulation of the neurohypophysis causes the mitotic rate in pituicytes to increase. 

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