The presence of many salts, such as sodium chloride, can adversely affect the performance of native electrospray ionization mass spectrometry for the analysis of proteins and protein complexes by reducing the overall molecular ion abundances and distributing signal for any given charge state into many cationized forms with various numbers of adducts attached. Several solution additives, such as ammonium bromide, ammonium iodide, and NaSbF(6), can significantly lower the extent of sodium ion adduction to the molecular ions of proteins and protein complexes. For ubiquitin, addition of 25 mM ammonium bromide or ammonium iodide into aqueous solutions also containing 1.0 mM NaCl results in a factor of 72 and 56 increase, respectively, in the relative abundances of the fully protonated molecular ions compared to when these additives are not present. The effectiveness of this method for reducing sodium ion adduction is related to the low proton affinity (PA) values of the anions. Anions with very low PA also have a propensity to adduct as an acid molecule, but these adducts can be readily dissociated from the molecular ions either by activation in the source or subsequently by collisional activation in the mass spectrometer. This method of reducing sodium ion adduction to proteins is simple and requires no experimental modifications, making it an attractive alternative to other methods for desalting proteins prior to mass spectrometry analysis.
The presence of many n class="Chemical">salts, such as n>n class="Chemical">sodium chloride, can adversely affect the performance of native electrospray ionization mass spectrometry for the analysis of proteins and protein complexes by reducing the overall molecular ion abundances and distributing signal for any given charge state into many cationized forms with various numbers of adducts attached. Several solution additives, such as ammonium bromide, ammonium iodide, and NaSbF(6), can significantly lower the extent of sodium ion adduction to the molecular ions of proteins and protein complexes. For ubiquitin, addition of 25 mM ammonium bromide or ammonium iodide into aqueous solutions also containing 1.0 mM NaCl results in a factor of 72 and 56 increase, respectively, in the relative abundances of the fully protonated molecular ions compared to when these additives are not present. The effectiveness of this method for reducing sodium ion adduction is related to the low proton affinity (PA) values of the anions. Anions with very low PA also have a propensity to adduct as an acid molecule, but these adducts can be readily dissociated from the molecular ions either by activation in the source or subsequently by collisional activation in the mass spectrometer. This method of reducing sodium ion adduction to proteins is simple and requires no experimental modifications, making it an attractive alternative to other methods for desalting proteins prior to mass spectrometry analysis.
Authors: Yihan Shao; Laszlo Fusti Molnar; Yousung Jung; Jörg Kussmann; Christian Ochsenfeld; Shawn T Brown; Andrew T B Gilbert; Lyudmila V Slipchenko; Sergey V Levchenko; Darragh P O'Neill; Robert A DiStasio; Rohini C Lochan; Tao Wang; Gregory J O Beran; Nicholas A Besley; John M Herbert; Ching Yeh Lin; Troy Van Voorhis; Siu Hung Chien; Alex Sodt; Ryan P Steele; Vitaly A Rassolov; Paul E Maslen; Prakashan P Korambath; Ross D Adamson; Brian Austin; Jon Baker; Edward F C Byrd; Holger Dachsel; Robert J Doerksen; Andreas Dreuw; Barry D Dunietz; Anthony D Dutoi; Thomas R Furlani; Steven R Gwaltney; Andreas Heyden; So Hirata; Chao-Ping Hsu; Gary Kedziora; Rustam Z Khalliulin; Phil Klunzinger; Aaron M Lee; Michael S Lee; Wanzhen Liang; Itay Lotan; Nikhil Nair; Baron Peters; Emil I Proynov; Piotr A Pieniazek; Young Min Rhee; Jim Ritchie; Edina Rosta; C David Sherrill; Andrew C Simmonett; Joseph E Subotnik; H Lee Woodcock; Weimin Zhang; Alexis T Bell; Arup K Chakraborty; Daniel M Chipman; Frerich J Keil; Arieh Warshel; Warren J Hehre; Henry F Schaefer; Jing Kong; Anna I Krylov; Peter M W Gill; Martin Head-Gordon Journal: Phys Chem Chem Phys Date: 2006-06-12 Impact factor: 3.676