Zaia J, Annan R S, Biemann K
Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139.
Rapid Commun Mass Spectrom. 1992 Jan;6(1):32-6. doi: 10.1002/rcm.1290060108.
Myoglobins from horse heart muscle, horse skeletal muscle and sperm whale are widely used as calibration standards or test compounds for various mass spectrometric methodologies. In all such cases reported in the literature, a molecular weight value is used (16,950.5 and 17,199, 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 reported to be +/- 0.01% and for electrospray ionization +/- 0.0025%, and error of one mass unit in approximately 17,000 would be significant. The mass-to-charge ratio 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 spectra 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 myoglobin is 16,951.49 and that of the sperm whale protein is 17,199.91.
来自马心肌、马骨骼肌和抹香鲸的肌红蛋白被广泛用作各种质谱分析方法的校准标准品或测试化合物。在文献报道的所有此类案例中，所使用的分子量值（分别为16,950.5和17,199）是基于这样一种假设，即这种由153个氨基酸组成的蛋白质中的第122位氨基酸是天冬酰胺，而忽略了已发表的一种观点，即它实际上是天冬氨酸。由于据报道基质辅助激光解吸质谱的质量分配精度为±0.01%，电喷雾电离为±0.0025%，在大约17,000的分子量中一个质量单位的误差将是显著的。来自市售马心肌和马骨骼肌肌红蛋白、后者的脱辅基肌红蛋白以及抹香鲸肌红蛋白的胰蛋白酶肽和胰凝乳蛋白酶肽的离子质荷比证明，在这两种蛋白质中第122位氨基酸确实是天冬氨酸，而非天冬酰胺。这一发现通过马肌红蛋白胰蛋白酶肽的[M + H]+离子和抹香鲸肌红蛋白胰凝乳蛋白酶肽的碰撞诱导解离光谱得到了进一步证实。因此，马肌红蛋白的正确分子量为16,951.49，抹香鲸蛋白质的正确分子量为17,199.91。
