Journal Article

Structural characterization by mass spectrometry of hemoglobin adducts formed after <i>in vitro</i> exposure to methyl bromide

Pasquale Ferranti, Nicola Sannolo, Gianfranco Mamone, Immacolata Fiume, Virginia Carbone, Margareta Tornqvist, Ake Bergman and Antonio Malorni

in Carcinogenesis

Volume 17, issue 12, pages 2661-2671
Published in print December 1996 | ISSN: 0143-3334
Published online December 1996 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/17.12.2661
Structural characterization by mass spectrometry of hemoglobin
                    adducts formed after in vitro exposure to methyl
                    bromide

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A mass spectrometric procedure is described for the structural study of the adducts formed in human hemoglobin by in vitro exposure of erythrocytes to the alkylating agent methyl bromide using different protein to reagent ratios. Peptide mapping by HPLC and tandem mass spectrometry allowed location of methylated amino acids within the protein sequence. A prominent reactivity of several nucleo-philic side chains in human hemoglobin summits was observed, which was modulated by the concentration of the alkylating agent Cysteine residues, the main reactive sites, were fully methylated in hemoglobin exposed to a 10-fold excess of methyl bromide, differently from other residues, including histidines, showing a heterogeneous pattern of methylation that was largely directed by their environment. No evidence of methylation was found at the heme proximal histidines β92 and α87. A more selective methylation was obtained when the ratio methyl bromide: hemoglobin was lowered to about 1: 1. In this last case only specific residues were reactive. Among them, the N-terminal amino group of both α- and β-globins, cysteine 104 in the α-chain and cysteine 93 (not cysteine 112) in the β-chain, indicating a different accessibility to reaction of the sulf-hydryl groups on the protein chain. Thus hemoglobin side chains are selectively modified and the degree of modification at each site is a function of the position of the single amino acid residue within the protein quaternary structure, raising the possibility that alterations of structure and functional properties of human hemoglobin following exposure to alkylating agents may be mediated through such covalent protein modifications. The results obtained demonstrate the usefulness of the analytical approach for the characterization of hemoglobin adducts with methyl bromide or similar compounds, which can constitute the basis for biomonitoring of human exposure.

Journal Article.  0 words. 

Subjects: Clinical Cytogenetics and Molecular Genetics

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