Granin - Derived Peptides in the Eye

The granins are the acidic proteins of secretory granules and there exist three main members of this family, in particular chromogranin A, chromogranin B and secretogranin II. These proteins are widely distributed throughout neuroendocrine tissues and are stored in large dense core vesicles in neuronal cells. Their functional role is not fully clear but it seems that they might play an important role in the formation of secretory granules. Furthermore, the primary amino acid sequence of the granins features many pairs of basic amino acids and these pairs together with monobasic residues are targets of enzymes which proteolytically process the proteins, in particular the prohormone convertases 1 and 2. Thus the granins might be precursors of smaller fragments and they are indeed cleaved.