Electrospray mass spectrometry of hydrophobic compounds using dimethyl sulfoxide and dimethylformamide as solvents

The use of dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) as solvents in electrospray ionization (ESI) is suggested for the analysis of hydrophobic compounds. Its use was shown to overcome solubility problems and resulted in good quality electrospray spectra of protected hydrophobic peptides, sugars and other hydrophobic compounds. Intense protonated and/or sodiated molecules were formed in positive ion mode while negative ion mode resulted in [M + 95](-) ions from DMSO and [M + Cl](-) ions from DMF in cases where no significant molecular ion related peaks could be observed applying commonly used protic solvents such as methanol or acetonitrile. Deuterium labeling (d6-DMSO), high resolution experiments and tandem mass spectrometric measurements showed that the methanesulfonic acid (MSA), present in DMSO as a common impurity, is responsible for the formation of protonated molecules in positive ion mode and for methane sulfonate anion adducts [M + 95](-) in negative ion mode.

Identification of ethyl pyruvate and dihydrocinchonidine adducts by electrospray ionization mass spectrometry

Several ethyl pyruvate and dihydrocinchonidine adducts, formed by non-covalent interactions with alkali cations, have been identified for the first time using electrospray ionization mass and tandem mass spectrometry. This type of adduct may have an important role in asymmetric reactions of pyruvates in the presence of cinchonas.

Identification of factor C protein from Streptomyces griseus by microelectrospray mass spectrometry

Factor C, an extracellular signal protein of cellular differentiation, was studied and significant homology was found to several zinc finger-type regulatory proteins. The complete amino acid sequence, deduced from the gene, that encodes the protein, did not support the hypothesis that this protein might be a zinc finger-type regulatory protein. However, a theoretical single nucleotide insertion in the gene can result in another similarly sized protein containing about 20 His residues, which would be responsible for the high zinc affinity of factor C. The protein sample was reduced, alkylated and then in-gel digested with trypsin. The peptide fragments were then separated by capillary chromatography and identified by microelectrospray mass spectrometry. Peaks of higher intensity were sequenced by tandem mass spectrometry. The identified peptide fragments and the measured molecular mass of factor C protein also confirmed the original sequence of protein, as there was no shift in the open reading frame.

Capillary chromatography/microelectrospray mass spectrometry used for the identification of putative cyclin-dependent kinase inhibitory protein in Medicago

A home-built capillary chromatography/microelectrospray system was used for peptide mass mapping of a putative cyclin-dependent kinase inhibitor protein with molecular mass of 8.5 kDa. The masses of identified tryptic fragments were then input to a protein database search routine. Daughter ion scans were done only on the most abundant tryptic fragments. On the basis of protein database search results and tandem mass spectrometric measurements the bioactive protein was identified as ubiquitin.