Effects of salts on the charge-state distribution and the structural basis of the most-intense charge-state of the gaseous protein ions produced by electrospray ionization

The charge-state distribution in the electrospray ionization mass spectra (ESI-MS) of different proteins in the absence and presence of various partially volatile salts such as ammonium sulphate, potassium acetate and ammonium acetate as well as in the presence Of some non-volatile salts are reported. The effects of the salts on the charge-states of the proteins elucidated the protein-salt particle interactions and the charge-transfer reaction that is recognized as an important mechanism of protonation or deprotonation of proteins. These results also indicated that the surface accessibility of the polar residues is an important factor for the interaction between the protein and the salt particles. The present studies could show a nice correlation of the most-intense charge-state of the gaseous protein ions with the surface exposed free basic (SEFBR) and free acidic (SEFAR) residues obtained from the crystal structures of the proteins. (C) 2009 Elsevier B.V. All rights reserved.