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Protein Profiling of Animal Tissues Using LAESI-MS

A method for imaging proteins using Laser Ablation Electrospray Mass Spectrometry (LAESI®-MS) is presented. Direct protein profiling of frozen whole body mouse tissue samples (taken directly from -80OC storage) is compared to tissues that are thawed, desiccated and subjected to lipid removal before analysis. Protein and peptide signal is shown to be greatly affected by the presence of lipids on the tissue sections. Presented here are mass spectra and mass spectrometry imaging (MSI) ion maps of intact proteins resulting from the LAESI-MS analysis. The protein ion maps from the LAESI-MS analysis are also compared to ion maps from MALDI-TOF-MS protein imaging for whole body mouse sections. The results show that LAESI-MS generates ESI- like protein charge envelopes, a characteristic that allows specific charged states to be targeted for fragmentation and for top-down sequencing. The ability to image proteins using LAESI-MS is greatly beneficial because sequence information for select proteins can potentially be obtained during an imaging experiment using mass spectrometers capable of top-down protein sequencing to confirm the identities of the proteins. (see Oral presentation TOB: Mass Spectrometry Imaging with LAESI hybrid ion trap FT-ICR mass spectrometer).

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