Multiply charged negative ions by electrospray ionization of polypeptides and proteins

• Published in: Analytical chemistry (Washington) Vol. 64; no. 1; pp. 81 - 88
• Main Authors: Loo, Joseph A, Loo, Rachel R. Ogorzalek, Light, Karen J, Edmonds, Charles G, Smith, Richard D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.01.1992
• Subjects: Adrenocorticotropic Hormone - chemistry; analysis; Analytical biochemistry: general aspects, technics, instrumentation; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Caseins - chemistry; Chemistry; Concanavalin A - chemistry; Cyclodextrins - chemistry; Fundamental and applied biological sciences. Psychology; Humans; Hydrogen-Ion Concentration; Ions; mass spectrometry; Mass Spectrometry - methods; Myoglobin - chemistry; Pepsin A - chemistry; Pepsinogens - chemistry; Peptides - chemistry; Proteins; Proteins - chemistry; Scientific imaging; Serum Albumin - chemistry; Proteins; Method; Aqueous solution; Mass spectrometry; Chemical ionization; Electrospray; Structural analysis
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac00025a015

Multiply deprotonated polypeptide and protein molecules, (M - nH)n-, produced from pH approximately 11 aqueous solutions, are analyzed by electrospray ionization-mass spectrometry (ESI-MS). Aqueous ammonium hydroxide solutions of the analyte are shown to be preferable to sodium hydroxide solutions for negative-ion ESI due to the production of multiply sodiated protein species from the latter system. Proteins with Mr to 66,000 and having up to 57 negative charges have been detected. Multiply charged negative ions can be produced from ESI of the highly acidic protein pepsin (Mr approximately 34,600) because of its relatively large number of acidic residues, 42. In contrast, the small number of basic amino acid residues for pepsin (4) does not allow formation of highly protonated species essential for positive-ion detection, for mass spectrometers of limited m/z range. Similarly, negative-ion ESI-MS is extended to large oligosaccharide analysis. Preliminary tandem mass spectrometry experiments of multiply charged polypeptide anions demonstrate the utility and potential of negative-ion ESI-MS for structural elucidation.