Mass spectrometric identification of phosphorylated vasostatin II, a chromogranin A-derived protein fragment (1-113)

Vasostatin II, an N-terminal chromogranin A-derived protein (CGA1-113), was purified from bovine chromaffin granule lysate and characterized by electrospray mass spectrometry (ES/MS) as being partially phosphorylated. The phosphorylation site was determined to be at the Ser81 position by mass spectrometric peptide mapping and tandem mass spectrometric analysis. This phosphorylation site is close to the processing site (...QKK78HSS(p)81...) yielding vasostatin I, an N-terminal CGA-derived peptide comprising residues 1-76, suggesting that phosphorylation at Ser81 is involved in the formation of vasostatin I in chromaffin cells.