MASS-SPECTROMETRIC IDENTIFICATION OF PHOSPHORYLATED VASOSTATIN-II, A CHROMOGRANIN A-DERIVED PROTEIN-FRAGMENT (1-113)

Vasostatin II, an N-terminal chromogranin A-derived protein (CGA(1-113 )), was purified from bovine chromaffin granule lysate and characteriz ed by electrospray mass spectrometry (ES/MS) as being partially phosph orylated. The phosphorylation site was determined to be at the Ser(81) position by mass spectrometric peptide mapping and tandem mass spectr ometric analysis. This phosphorylation site is close to the processing site (...QKK(78)HSS(p)(81)...) yielding vasostatin I, an N-terminal C GA-derived peptide comprising residues 1-76, suggesting that phosphory lation at Ser(81) is involved in the formation of vasostatin I in chro maffin cells. (C) 1997 Elsevier Science B.V.