A sialylation study of mouse brain gangliosides by MALDI a-TOF and o-TOF mass spectrometry.

Matrix-assisted laser desorption/ionization (MALDI) process of sialoglycoconjugates is generally accompanied by different levels of cleavage of sialic acid residues and/or by dehydration, and decarboxylation reactions. Quantitative densitometry of the mouse brain ganglioside (MBG) components separated by high-performance thin layer chromatography (HPTLC) and evidenced by orcinol staining was a basis to verify the ganglioside composition pattern with respect to the relative abundances of individual components in the mixture. A systematic mass spectrometry (MS) sialylation analysis has been carried out to evaluate the feasibility of an axial time-of-flight (a-TOF) MS, equipped with a vacuum MALDI source and an orthogonal-TOF (o-TOF) instrument with an ion source operated at about 1 mbar of N(2). Besides, the esterification by one methyl group of the carboxyl group in sialic acid to increase the stability of the ganglioside species for MALDI MS analysis has been tested and the yield of intact ganglioside species and of the neutral loss of water and carbon dioxide estimated. For the sialylation analysis of native ganglioside mixtures the MALDI o-TOF analysis with 6-azo-2-thiothymine/diammonium citrate (ATT/DAC) as a matrix appears as an optimal approach for ganglioside profiling.