Accurate mass measurement and tandem mass spectrometry of intact globin chains identify the low proportion variant hemoglobin Lepore–Boston–Washington from the blood of a heterozygote

AbstractWithin a mixture of proteins, minor polymorphic components are difficult to identify using a conventional proteomic approach. Their identification generally requires multi‐dimensional separation steps, before or after proteolytic cleavage, followed by sequence analysis of the proteolytic products. In this study, we investigated the potential of tandem mass spectrometry for protein characterization by identifying the δ–β hybrid human hemoglobin variant Lepore–Boston–Washington using electrospray ionization tandem mass spectrometry. Hemoglobin Lepore–Boston–Washington occurs mainly in heterozygotes, where it comprises ∼10% of the total non‐α‐chains, the dominant non‐α‐chain being the normal β(∼90%). Furthermore, Hemoglobin Lepore–Boston–Washington has an average molecular mass (15 865.23 Da) that is only 2 Da lower than that of the normal β‐chain (15 867.24 Da). Consequently, it cannot be resolved from the normal β‐chain by mass spectrometry. Here we show how Hemoglobin Lepore–Boston–Washington was identified directly from the diluted blood of a heterozygote by analyzing the product ions from the Lepore–Boston–Washington and normal β‐chain ions without prior separation of the individual chains. This study shows the potential of the tandem mass spectrometry for identifying a minor component in an unseparated mixture of proteins. Copyright © 2004 John Wiley & Sons, Ltd.