Biomolecules electrospray mass spectrometry

Matrix-assisted laser desorption mass spectrometry (MALDI-MS) is, after electrospray ionization (ESI), the second most commonly used method for ionization of biomolecules in mass spectrometry. Samples are mixed with a UV-absorbing matrix substance and are air-dried on a metal target. Ionization and desorption of intact molecular ions are performed using a UV laser pulse. 

Numerous workers have demonstrated the applicability of electrospray ionization mass spectrometry (ESI/MS) for the detection and analysis of biomolecules with highly electronegative groups (reviewed by Wood et al., 2003, and for neutral steroids by Higashi and Shimada, 2004). The sensitivity of detection of neurosteroids can also be enhanced by derivatization when they are analyzed by nano-electrospray/mass spectrometry procedures. Neurosteroid sulfates can be easily prepared in a single-step reaction in pyridine with the N,N-dimethylformamide complex of sulfur trioxide (Chatman et al., 1999). Another elegant... 

In conjunction with XAS and other techniques, such as EPR spectroscopy for the characterization of Cr(V) complexes, electrospray mass spectrometry (ESMS) is an extremely useful tool. Often the parent peak for even reactive Cr(V) and Cr(Vl) complexes dominates the spectrum and allows important structural information to be elucidated (92, 93). In water, where complex mixtures are often involved, it is a useful technique to aid in the speciation of complexes, although the redox chemistry and the extensive fragmentation that tends to occur (94) means that the results need to be interpreted with care (usually in conjunction with other independent information on the speciation) (22, 23, 34, 95). Recently, ESMS has been applied to studies of biologically relevant Cr(lll) complexes (95) and Cr -DNA interactions (96). Thus, ESMS is applicable to all oxidation states and will no doubt contribute to further the characterization of reactive Cr species of relevance to cancer, dietary supplements, and naturally occurring Cr complexes with biomolecules. 

Hyphenation of chromatography and ICP-MS is especially important for work in the life sciences, as discussed by Jakubowski et al. [723] in an introductory paper to a special issue of the Journal of Analytical Atomic Spectrometry on the determination of metallobiomolecules. ICP-MS has great potential for work in proteomics [724], provided that the biomolecules can be identified by NMR or electrospray organic mass spectrometry. The determination of protein phosphorylation, for example, has been shown to be readily possible by liquid chromatography coupled to elemental mass spectrometry with P detection and to electrospray mass spectrometry, as shown in Ref [725]. In order to cope with the danger of transformations of species, isotopic labeling is very helpful, but it can only be used to its full potential... 

Pulsed ultrafiltration, when coupled to electrospray mass spectrometry, may be used to analyze ligand/biomolecule interactions [45]. As proof of principle, a small library of adenosine deaminase... 

Fenn J.B., Mann M., Meng C.K., Wong S.F., and Whitehouse C.M. (1989), Electrospray ionization for mass spectrometry of large biomolecules, Science 246, 64-71. 

Choudhary, G., Horvath, C., and Banks, J. E (1998). Capillary electrochromatography of biomolecules with online electrospray ionization and time-of-flight mass spectrometry.. Chromatogr. A 828, 469—480. 

Hutton, T. and Major, H.J., Characterizing biomolecules by electrospray ionization-mass spectrometry coupled to liquid chromatography and capillary electrophoresis, Biochem. Soc. Trans., 23, 924, 1995. 

Two recently developed mass spectrometric techniques have had a major impact on the analysis of large biomolecules matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS). MALDI-MS was first introduced by Karas and Hillenkamp66 and Tanaka et al.61 in 1988 and has experienced an exponential development. It has become a widespread soft ionization technique for bioorganic samples, especially large biomolecules. Fenn and co-workers68 first published the successful soft ionization technique for... 

Mass spectrometry has been revolutionalized by the advent of electrospray ionization, but, before we concentrate on this relatively recent addition to the array of ionization methods, we will first discuss two other techniques which are routinely used for the ionization of biomolecules matrix assisted laser desorption ionization (MALDI) and fast atom bombardment (FAB). These techniques share common features in that ... 

Reversed-phase HPLC is widely utilized to generate a peptide map from digested protein, and the MS online method provides rapid identification of the molecular mass of peptides. The HPLC-MS-FAB online system is a sensitive and precise method for low-MW peptides (<3000 Da) even picomol quantities can be detected. However, as the MW of the analytes increases, the ionization of peptides becomes more difficult and decreases the sensibility of the FAB-MS (112). Electrospray ionization (ESI-MS) was found to be an efficient method for the determination of molecular masses up to 200,000 Da of labile biomolecules, with a precision of better than 0.1%. Molecular weights of peptide standards and an extensive hydrolysate of whey protein were determined by the HPLC-MS-FAB online system and supported by MALDI-TOF (112). Furthermore, HPLC-MS-FAB results were compared with those of Fast Performance Liquid Chro-motography (FPLC) analysis. Mass spectrometry coupled with multidimensional automated chromatography for peptide mapping has also been developed (9f,l 12a). 

Fenn JB, Mann M, Meng CK Electrospray ionization for mass spectrometry of large biomolecules. Science (1989) 246 64-71. Patrick JS, Lagu AL Review applications of capillary electrophoresis to the analysis of biotechnology-derived therapeutic proteins. Electrophoresis (2001) 22 4179-4196. Sowell J, Salon J, Strekowski L, et al Covalent and noncovalent labeling schemes for near-infrared dyes in capillary electrophoresis protein applications. Methods Mol. Biol. (2004) 276 39-75. Moini M Capillary electrophoresis mass spectrometry and its application to the analysis ofbiological mixtures. Anal. Bio-anal. Chem. (2002) 373 466 180. Nemunaitis J, Holmlund JT, Kraynak M, et al. Phase I evaluation of ISIS 3521, an antisense oligodeoxynucleotide to protein kinase C-a, in patients with advanced cancer./. Clin. Oncol. (1999) 17 3586-3595. De Frutos M, Cifuentes A, Diez-Masa JC Differences in capillary electrophoresis profiles of urinary and recombinant erythropoietin. Electrophoresis (2003) 24 678-680. 

At the beginning of the 1990s, two new ionization methods, electrospray ionization (ESI) [9] and matrix-assisted laser desorption/ionization (MALDI) coupled to time-of-flight (TOF) analysers [10] that avoided such inconveniences, were developed and continue to revolutionize the role of mass spectrometry in biological research. These methods allow the high-precision analysis of biomolecules of very high molecular weight. 

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