Subject MALDI

The results for bacterial whole-cell analysis described here establish the utility of MALDI-FTMS for mass spectral analysis of whole-cell bacteria and (potentially) more complex single-celled organisms. The use of MALDI-measured accurate mass values combined with mass defect plots is rapid, accurate, and simpler in sample preparation then conventional liquid chromatographic methods for bacterial lipid analysis. Intact cell MALDI-FTMS bacterial lipid characterization complements the use of proteomics profiling by mass spectrometry because it relies on accurate mass measurements of chemical species that are not subject to posttranslational modification or proteolytic degradation. 

Imaging mass spectrometry involves MS performed on tissue sections mounted on a MALDI plate. The mass spectra generate images and an in situ protein expression profile of the specimen is analyzed. Specifically, the frozen tissue sections applied to a MALDI plate are subjected to laser interrogation and analyzed at regular spatial intervals. The mass spectral data obtained at different intervals are compared to generate a spatial distribution of masses (proteins) across the tissue section. 

There is a recent hybrid between AP-MALDI and ESI, matrix-assisted laser desorption electrospray ionization (MALDESI) [202], where species desorbed from a MALDI target are subjected to an electrospray before entering the mass spectrometer. The method is similar to ELDI except that the analyte is embedded in a matrix as in MALDI. 

The mechanisms of ion formation in MALDI are a subject of continuing research. [30-34] The major concerns are the relationship between ion yield and laser flu-ence, [28,35] the temporal evolution of the desorption process and its implications upon ion formation, [36] the initial velocity of the desorbing ions, [29,37,38] and the question whether preformed ions or ions generated in the gas phase provide the major source of the ionic species detected in MALDI. [39,40]... 

Recent advances in mass spectrometry (MS) technology have provided researchers with an unparalleled ability to identify the types and patterns of secondary biochemical modifications found on proteins in living cells. Matrix-assisted laser desorption/ionization-MS (MALDI-MS) analyses have shown, for example, that HMGA proteins in vivo are simultaneously subject to complex patterns of phosphorylation, acetylation and methylation and that, within the same cell type, different isoforms of these proteins can exhibit quite different modification patterns [33]. Furthermore, these in vivo modifications have been demonstrated to markedly alter the binding affinity of HMGA proteins for both DNA and chromatin substrates in vitro [33]. Nevertheless, due to their number and complexity, it has been difficult to determine the actual biological function(s) played by these biochemical modifications in living cells. 

The 1 1 mixtures of strands 19 and 20 (0.5 mM each) were prepared in CH2CI2, methanol, and water. The samples were subjected to redox conditions (I2) for various lengths of time and then examined by matrix assisted laser desorption ionization (MALDI). As expected, 19 and 20 sequence specifically associated with each other in CH2CI2, leading to the disulfide cross-linked 19-20 as the major product. With an increasing ratio of methanol in CH2CI2, the cross-linked 19-20 stUl appeared as the dominant product. The same phenomenon was observed in pure methanol and even in water (Fig. 9.14b). The sequence dependence of the cross-linking of 19 and... 

Figure 9.14 (a) Complementary strands 19 and 20 carrying trityl-protected thio groups can be cross-linked when subjected to reversible redox conditions, (b) MALDI spectra show that 19 and 20 were sequence specifically cross-linked into 19-20 in both methanol and water. 

In direct introduction the sample can be introduced via a sample probe or plate through a vacuum lock, and can subsequently be ionized via El, Cl or matrix-assisted laser desorption ionization (MALDI see Section 2.4). Alternatively, the sample can be introduced as a liquid stream into an ion source at atmospheric pressure, after which it is subjected to electrospray ionization (ESI see Section 2.3). Direct injection does not offer any form of sample separation. 

MALDI-TOF/TOF MS to successfully study the carbonylation of sarcoplasmic and myofibrillar proteins from fish subjected to metal-catalyzed oxidation (98). 

Chiral recognition by calixarenes in the gas phase is virtually unknown.458-460 To date, only few very recent gas-phase studies on this subject can be retrieved from the literature, i.e., (i) a gas-phase study on the displacement of several amino acids from the chiral amido4resorcinarene 9 (Scheme 9) carried out by Speranza and coworkers using an electrospray-ionization Fourier-transform ion cyclotron resonance (ESI-FT-ICR) mass spectrometer,461 462 and (ii) Lebrilla and coworkers study on the ability of the achiral calix[4]arene 7 and calix[6]arene 8 to form inclusion complexes with natural amino acids under matrix-assisted laser desorption ionization (MALDI) conditions.459... 

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