Accelerated Art ides Anal. Chem. 1994,66, 3289-3296
Electrospray Mass Spectrometric Study of Protein-Ketone Equilibria in Solution J. C. Y. Le Bianc,f K. W. M. Siu,’ and Roger Guevremont Institute for Environmental Research and Technology, National Research Council of Canada, Montreal Road, Ottawa, Ontario, Canada K1A OR6 The electrospray mass spectra of basic protein solutions containingketones exhibit ions that are attributableto proteinketone adducts whose relative abundances are in accordance with the relative concentrations of these adducts in solution. In a basic solution, the deprotonated (neutral) amino groups in a protein may be alkylated by ketone molecules to form Schiff bases. The extent of alkylation may be approximated by statistics if the reactivity of each amino group is identical. The relative ion abundances of these adducts have been found to follow their statistical distributions expected in solution. The reaction to form Schiff bases may be applied to the measurementof the number of primary aminosites (N-terminus plus lysine residues) in a protein. Excellent agreement with known numbers was observed for all 18 proteins measured. Since Fenn and co-workers’l first demonstration of the analytical capabilities of electrospray mass spectrometry, the application of this technique has increased significantly, especially in the bioanalytical field. The ability to desorb multiply charged ions of high molecular mass compounds from aqueous solutions, and to mass analyze them using quadrupole filters whoseupper m/z limits arecomparatively low (
