Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 61, Issue 2, Pages 418-426Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf303973b
Keywords
riboflavin; alpha-lactalbumin; immuno-spin trapping; mass spectrometry; oxidation mechanism
Funding
- Danish Agency of Science, Technology and Innovation
- Proteins as Antioxidants - Effect of Protein Structure
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Free radicals and other oxidation products were characterized on a-lactalbumin with electron spin resonance (ESR), immuno-spin trapping, and mass spectrometry (MS) after riboflavin-mediated oxidation. Radicals were detected using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in immuno-spin trapping with both enzyme-linked immunosorbent assay (ELISA) and Western blotting and further characterized with mass spectrometry. A DMPO-trapped radical was identified at His68 and another at one of the tyrosine residues, Tyr50 or Tyr36, respectively, generated by a type II or I mechanism. Not all tyrosyl radicals were trapped, as the secondary oxidation product, 3,4-dihydroxyphenylalanine (DOPA), was detected by mass spectrometry at Tyr18 and Tyr50. A further oxidation of DOPA resulted in the DOPA o-semiquinone radical, which was characterized by ESR. Both surface exposure and the neighboring residues in the local environment of the tertiary structure of alpha-lactalbumin seem to play a role in the generation of DMPO trapped radicals and secondary oxidation products.
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