Specific reaction of Met 35 in amyloid beta peptide with hypochlorous acid

The reaction of the amyloid beta peptide (A beta) with hypochlorous acid and hydroxyl radicals was analysed by spectrophotometry and mass spectrometry. N-acetylmethionine, A beta 25-35 and A beta 1-42 reacted rapidly with hypochlorous acid. The relative reaction rates of N-acetylmethionine and A beta with hypochlorous acid was in the order N-acetylmethionine > A beta 25-35 > A beta 1-42. While the reaction of A beta 25-35 in the presence of a slight excess of hypochlorous acid resulted in complete conversion of Met35 to Met35 sulphoxide, A beta 1-42 required more than a 4-fold excess of hypochlorous acid for complete conversion of Met35. Identical products were obtained when A beta 25-35 and A beta 1-42 were treated with a hypochlorous acid generating system. Conversion of Met35 to Met35 sulphoxide in A beta abolished the aggregation of A beta 25-35. Reaction of A beta with hydroxyl radicals resulted in limited conversion of Met35 to Met35 sulphoxide. The specific reaction of Met35 in A beta with hypochlorous acid to form Met35 sulphoxide has been analysed.