MATRIX-ASSISTED LASER DESORPTION IONIZATION MASS-SPECTROMETRY (MALDI-MS) OF MEMBRANE-PROTEINS AND NONCOVALENT COMPLEXES/

Matrix-assisted laser desorption/ionization (MALDI) mass spectra and m ethods to improve their quality are reported for three hydrophobic, me mbrane-bound proteins: porin from Escherichia coli, bacteriorhodopsin from Halobacterium salinarium and cholesterolesterase from Pseudomonas fluorescens. Several commonly used UV and IR matrices have been teste d. In addition, the susceptibility of MALDI mass spectrometry to vario us neutral and ionic detergents, known usually to degrade the quality of MALDI mass spectra, has been tested systematically, For porin, cons isting of three identical non-covalently bound subunits, a new sample preparation is reported, resulting in the desorption of the intact qua ternary protein structure. This leads to a better understanding of the way a given analyte is embedded into the host matrix crystals.