Carbamino group formation with peptides and proteins studied by mass spectrometry

Abstract

At high pH and in the presence of dissolved CO 2 , the N-terminus and -amino groups of amino acids, peptides, and proteins can form carbamino adducts with CO 2 , R-NH 2 ϩ CO 2 ↔ R-NHCOO Ϫ ϩ H ϩ . We report the first study of carbamino group formation by electrospray ionization (ESI) mass spectrometry (MS). Angiotensin II, bradykinin, substance P, and insulin have been studied. A careful optimization of the instrumental parameters was necessary to allow the transfer of the fragile adducts into vacuum for mass analysis. Particularly, dissociation of the adducts in the ion sampling process and pH changes in ESI must be minimized. With these precautions, levels of carbamino group formation of angiotensin II and bradykinin determined from mass spectra agree with those expected to be in solution, calculated from literature equilibrium constants. Thus, ESI MS can quantitatively measure ratios of carbamino adduct to total peptide concentration in solution. Values of equilibrium constants for carbamino group formation with substance P (pK c ϭ 4.77 Ϯ 0.18) and insulin (pK c ϭ 4.99 Ϯ 0.05) are reported for the first time. (J Am Soc Mass Spectrom 2010, 21, 1500 -1505

Tandem Mass Spectrometry Measurement of the Collision Products of Carbamate Anions Derived from CO2 Capture Sorbents: Paving the Way for Accurate Quantitation

“…Aside from carbamino protein adducts (proteins with a carboxylated N-terminus) [41] and a recent pre-dissociative vibrational study of piperidine-1-carboxylate [42], there is little information pertaining to hydrolyzed or anionic carbamates in the open literature. The carbamate anions discussed in this work should not be confused with esterified carbamates (NHR-C(=O)OR'), which find widespread application as pesticides and for which there are well-developed techniques for their analysis and quantitation using both GC- and LC-MS [43, 44].…”

The identification of carbon dioxide mediated protein post-translational modifications

“…The lability of such exchangeable carbamates outside of the cellular environment makes the identification of this PTM a significant analytical challenge. Soft ionisation mass spectrometry techniques have had limited success in demonstrating the presence of carbamate PTMs but were unable to identify locations of modification 24 .…”

Observation of CO2 and solvent adduct ions during negative mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric analysis of monohydric alcohols

“…It is common to find [M + methanol – H] – ions in negative ion ESI mass spectra, due to the tendency of methanol to form hydrogen bonds with analyte molecules. It has been reported that at high pH values and in the presence of dissolved CO 2 the N ‐terminus and ε ‐amino groups form adducts with CO 2 . However, the formation of adduct ions (O3 species) from the hydroxyl group of alcohols and CO 2 has not been reported.…”

“…It has been reported that at high pH values and in the presence of dissolved CO 2 the N-terminus and ε-amino groups form adducts with CO 2 . [8,9] However, the formation of adduct ions (O3 species) from the hydroxyl group of alcohols and CO 2 has not been reported.…”