Reactivity and mechanism of the reactions of 4-methylbenzoquinone with amino acid residues in β-lactoglobulin: A kinetic and product investigation

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Quinones, produced by the oxidation of phenolic compounds, covalently bind to nucleophilic groups on amino acids or proteins. In this study, the reactions of 4-methylbenzoquinone (4MBQ) with β-lactoglobulin (β-LG) and amino acids at neutral pH were investigated. LC-MS analysis revealed that Cys121 was likely the most modified residue in β-LG. Identification of reaction products by LC-MS/MS showed that Michael addition occurred in all reactions with amino acids tested. The formation of Schiff base and a di-adduct was found in His and Trp samples. Apparent second-order rate constants (k2) were determined at 25 °C and pH 7.0 by stopped-flow spectrophotometry. The rate of reactions decreased in the order: β-LG > His > Trp > Arg > Nα-acetyl His > Nα-acetyl Arg > Nα-acetyl Trp. The rate constants correlated with the pKa values of the amino acids, showing that the amount of unprotonated amine is the major factor determining the reactivity.

Original languageEnglish
Article number137473
JournalFood Chemistry
Number of pages10
Publication statusPublished - 2024

Bibliographical note

Publisher Copyright:
© 2023 The Author(s)

    Research areas

  • 4-methylcatechol, Kinetics, Michael addition, Polyphenol-protein binding, Protein modification, β-lactoglobulin

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