Secretogranin-1 is a neuroendocrine secretory granule protein, which may be the precursor for other biologically active peptides. Neuroendocrine and endocrine secretory granules. Peptide SR-17 exists in both monophosphorylated and diphosphorylated forms. With 1 phosphate group. With 2 phosphate groups. Belongs to the chromogranin/secretogranin protein family. PubMed:11168356 reported the oxidation of Met-651 to sulfoxide. This is most probably an artifact of isolation.