The determination of an amino acid substitution in the "core" region of abnormal
hemoglobin is technically difficult and is time- and labor-intensive both by conventional and by mass spectrometry techniques. Underivatized subunits cleaved with
trypsin and
lysyl endopeptidase were analyzed by high-performance liquid chromatography-electrospray ionizationmass spectrometry. The core
peptides showed a series of multiply charged
ions of homo- and heterodimers. Abnormal
peptides in the core region could be detected in dimeric form. The sequence of core
peptides was determined by product ion spectra of the
peptides from oxidized
globin digested with
trypsin and
lysyl endopeptidase. Oxidation of
cysteine residues to cysteic
acids in the core region resulted in the strong promotion of y-series
ions by product ion analysis with a tryptic
peptide from
apoprotein B-100 as previously reported by Burlet, Yang, and Gaskell (J. Am. Soc. Mass Spectrom. 1992, 3, 337-344). These techniques were used to prove that substitution of an unstable
hemoglobin, known as
Hb Santa Ana (β88
leucine →
proline), occurred in a patient with
congenital hemolytic anemia. The tandem mass spectrometry analysis with oxidized
globin digested with
trypsin and
lysyl endopeptidase offers a novel method to detect substitutions in the core region of
hemoglobin.