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Denaturation of α ‐lactalbumin and ubiquitin studied by electrospray and laser spray
Author(s) -
Nakamura Masana,
Takamizawa Atsushi,
Yamada Hideki,
Hiraoka Kenzo,
Akashi Satoko
Publication year - 2007
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2995
Subject(s) - chemistry , denaturation (fissile materials) , electrospray , protonation , amide , raman spectroscopy , aqueous solution , lactalbumin , ubiquitin , mass spectrometry , chromatography , analytical chemistry (journal) , crystallography , ion , organic chemistry , nuclear chemistry , biochemistry , gene , physics , optics
Electrospray and laser spray mass spectra of human α ‐lactalbumin and bovine ubiquitin were studied, with an emphasis on the denaturation induced by laser spray. There were no remarkable differences in the electrospray and laser spray mass spectra for acidic and basic aqueous solutions of α ‐lactalbumin in positive and negative modes of operations. This originates from the fact that this protein is tightly folded with four disulfide bonds. For ubiquitin, however, denaturation was induced by laser spray for the positive mode of operation and the [M+nH] n+ with a maximum of n = 13 was observed, i.e., all the acidic amino acid residues are fully neutralized (protonated). In contrast, the laser‐induced denaturation was not observed for the negative mode of operation, i.e., denaturation of ubiquitin is largely suppressed in the negatively charged liquid droplets. The marked difference observed in the positive and negative modes of operations for ubiquitin is ascribed to the difference in the susceptibility of side‐chain/main‐chain interactions in the positive‐ion excess and in the negative‐ion excess liquid droplets. That is, the interactions between the basic residues and main‐chain amide carbonyl groups (NH 3 + •••OC< or NH 2 •••OC<) which play an important role in stabilizing the protein structures are not so affected in the negative mode of operation but are weakened in the positive mode of operation. Copyright © 2007 John Wiley & Sons, Ltd.