Gas-phase ion/ion reactions of multiply protonated polypeptides with metal containing anions.

Gas-phase reactions of multiply protonated polypeptides and metal containing anions represent a new methodology for manipulating the cationizing agent composition of polypeptides. This approach affords greater flexibility in forming metal containing ions than commonly used methods, such as electrospray ionization of a metal salt/peptide mixture and matrix-assisted laser desorption. Here, the effects of properties of the polypeptide and anionic reactant on the nature of the reaction products are investigated.

Effects of single amino acid substitution on the collision-induced dissociation of intact protein ions: Turkey ovomucoid third domain.

Expanded understanding of the factors that direct polypeptide ion fragmentation can lead to improved specificity in the use of tandem mass spectrometry for the identification and characterization of proteins. Like the fragmentation of peptide cations, the dissociation of whole protein cations shows several preferred cleavages, the likelihood for which is parent ion charge dependent. While such cleavages are often observed, they are far from universally observed, despite the presence of the residues known to promote them.

Generation and manipulation of sodium cationized peptides in the gas phase.

Sodiated peptides are often generated by electrospray ionization (ESI) of solutions containing peptides and a sodium salt. Fragmentation of singly sodiated, singly charged peptide ions commonly provides specific sequence information. However, these ions may be difficult to form by directly electrospraying a mixture.

Whole protein dissociation in a quadrupole ion trap: identification of an a priori unknown modified protein.

A protein mixture derived from a whole cell lysate fraction of Saccharomyces cerevisiae, which contains roughly 19 proteins, has been analyzed to identify an a priori unknown modified protein using a quadrupole ion trap tandem mass spectrometer. Collection of the experimental data was facilitated by collision-induced dissociation and ion/ion proton-transfer reactions in multistage mass spectrometry procedures. Ion/ion reactions were used to manipulate charge states of both parent ions and product ions for the purpose of concentrating charge into the parent ion of interest and to reduce the product ion charge states for determination of product ion mass and abundance.

Gas-phase peptide/protein cationizing agent switching via ion/ion reactions.

Polypeptide ions comprising different cationizing agents show distinct fragmentation behavior in the gas phase. Thus, it is desirable to be able to form ions with different cationizing agents such as protons and metal ions. Usually, metal-cationized peptide/protein ions are introduced to the mass spectrometer by electrospraying solutions containing a mixture of the peptide/protein of interest and a metal salt.