CHARACTERIZATION OF RIBONUCLEASE-B HETEROGENEITY AND THE IDENTIFICATION AND REMOVAL OF PHOSPHATE ADDUCTS BY HIGH-RESOLUTION ELECTROSPRAY-IONIZATION FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

New instrumentation based on the combination of electrospray ionizatio n (ESI) and Fourier transform ion cyclotron resonance (FTICR) mass spe ctrometry has been developed for the study of large biomolecules. The high resolution and accurate mass measurements possible with this inst rumentation are demonstrated by application to the heterogeneous glyco protein, Ribonuclease B (RNase B). The high resolution routinely attai nable allows unambiguous charge state assignments, and thus, precise m ass determination for all ions observed and demonstrates the utility o f ESI-FTICR for the analysis of complex biological mixtures. In additi on, results are presented for the dissociation of RNase B in both the electrospray source and in the ICR cell. The results show that phospha te adducts to RNase B molecular ions are most readily dissociated in t he heated capillary inlet, less effectively by collisional activation in the 1-10 Torr capillary-skimmer region, and with significantly redu ced efficiency by collisional activation in the ICR cell, where other dissociation processes dominate. This trend is correlated with the ext ent of molecular ion solvation expected in the three regions, and sugg ests that phosphate adduct removal is most effective for solvated mole cular ions.