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The correct molecular weight of myoglobin, a common calibrant for mass spectrometry
Author(s) -
Zaia Joseph,
Annan Roland S.,
Biemann Klaus
Publication year - 1992
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.1290060108
Subject(s) - myoglobin , chemistry , mass spectrometry , asparagine , sperm whale , chromatography , aspartic acid , amino acid , peptide , biochemistry
Myoglobins from horse heat muscle, horse skeletal muscle and sperm whale are widely used as calibration standards or test compounds for various mas spectrometric methodologies. In all such cases reproted in the literature, a molecular weight value is used (16950.5 and 17199, respectively) which is based on the assumption that amino acid 122 in this 153 amino‐acid‐long protein is asparagine, overlooking a published suggestion that it is aspartic acid instead. Since the mass assignment accuracy for matrix‐assisted laser desorption mass spectrometry is reproted to be ±0.01% and for electrospray ionization ±0.0025%, and error of one mass unit in ∼ 17000 would be significant. The mass‐to‐charge ration of ions of the tryptic peptide encompassing amino acid 122 derived from commercially available horse heart and horse skeletal myoglobins, the apomyoglobin of the latter, and the tryptic and chymotryptic peptide of sperm whale myoglobin proved that in both proteins amino acid 122 is indeed aspartic acid, rather than asparagine. This finding was further confirmed by the collision‐induced dissociation sectra of the [M+H]+ ions of the tryptic peptides from the horse myoglobins and the chymotriptic peptide from sperm whale myoglobin. Thus, the correct molecular weight of horse myoglobinis 16951.49 and that of the sperm whale protein is 17199.91.