FORMATION OF HOMO AND HETERO MULTIMERIC IONS OF LARGE PROTEINS IN MATRIX-ASSISTED UV LASER-DESORPTION IONIZATION

An investigation was performed to elucidate the formation of gas-phase homo and hetero multimeric ions in matrix-assisted UV laser desorptio n/ionization of large proteins and their mixtures. Such multimeric ion s with mass extending to about 250 x 10(3) Da, some consisting of up t o three large different proteins, were detected by linear time-of-flig ht mass spectrometry, following 337 nm laser irradiation of analyte sa mples embedded in a variety of matrices and at a range of matrix-analy te dilutions. The dependence of the extent of multimerization of prote in molecules on the analyte concentration and the fluence used for sam ple desorption was studied. The analysis of the results obtained revea led the existence of an optimum analyte concentration and a fluence th reshold for detecting multimeric ions, both parameters increasing with increasing mass of the relevant aggregates. The influence of sample m orphology on clustering was also examined, employing several different methods of sample preparation, multimerization being more pronounced with the simple dried droplet method.