Two possible improvements for mass spectrometry analysis of intact biomolecules.

The goals of our study were to investigate abilities of two approaches to eliminate possible errors in electrospray mass spectrometry measurements of biomolecules. Passing of a relatively dense supersonic gas jet through ionization region followed by its hitting the spray of the analyzed solution in low vacuum may be effective to keep an initial biomolecule structure in solution. Provided that retention of charge carriers for some sites in the biomolecule cannot be changed noticeably in electrospray ion source, decomposition and separation of charge-state distributions of electrosprayed ions may give additional information about native structure of biomolecules in solution.

Decomposition of charge-state distributions for a better understanding of electrospray mass spectra of bioorganic compounds. Part 1: basic formalism.

Further development in our approach for the interpretation of a mass spectral peak series resulting from unique modifications at a number of molecular sites is described and its application for the analysis of electrospray mass spectra of multiply-charged ions of biopolymers is specified. This method was based initially on the assumption that the modifications are mutually independent. The output is a set of modification probabilities for the considered molecular sites, which explains the observed peak intensity distribution with the best accuracy. It is shown here that the method is also applicable, in some cases, to the strong interaction between modified sites. This is important for the formation of multiply-charged ions, at least in the gas phase, since it should be significantly influenced by the internal electric fields. The capabilities and limitations of this approach are discussed. One limitation is that only unimodal distributions (those having only one maximum) are possible in the considered model. Another is that relatively large biomolecules may not be suitable for this type of analysis. Some experimental results of the application of this method are described in Part 2 of this work.

Decomposition of charge-state distributions for better understanding of electrospray mass spectra of bioorganic compounds. Part 2: application of the method.

The results of the analysis of electrospray mass spectra of b-endorphin and chicken egg lysozyme in different conditions of data acquisition using the method described in Part 1 of the work are reported. At least partial unfolding during the process of ion formation in the electrospray ion source of an initially native biomolecule of lyzozyme in solution should supposedly explain the received set of probabilities of proton retention by basic and acidic residues of this molecule for all considered conditions of data acquisition.