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Protein Protocols Protein Protocols

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688 Wada<br />

Fig. 5. FAB mass spectra of (A) tryptic and (B) endoproteinase Lys-C digests of an α-globin<br />

variant.<br />

Fig. 6. FAB mass spectrum of the tryptic digest of a β-globin variant.<br />

3.5.2. Complex Cases<br />

1. Characterization based on additional information: In cases in which the molecular weight<br />

of the mutated peptide does not permit the assignment of a unique type and/or position of<br />

substitution, chemical data, such as the charge carried on the variant, may provide an<br />

answer. In the mass spectrum of a tryptic digest of an α-globin shown in Fig. 8, a combined<br />

peptide T10+T11, which is normally present, at m/z 1087.6 owing to incomplete<br />

cleavage, is missing and a new peptide is observed at m/z 1059.6. The decrease of 28 Da<br />

suggests six possible mutations: Arg→Lys, Arg→Gln, Val→Ala, Asp→Ser, Glu→Thr,<br />

and Met→Cys. The first four substitutions are possible on the basis of the normal sequence

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