Stimulated neutrophils (PMNL) are a source of the active oxygen species: O2, H2O2 and HOCl/OCT which in turn can act on proteins yielding a variety of mixed oxidation products. A system is proposed in which a model protein — ovalbumin (OVA) first undergoes chlorination by HOC1/OCT and next is oxidised by H2O2. The modification of functional groups (-NH2, -SH, -S-S-, >C=0, Tyr and Trp) in OVA was monitored as well as their accessibility to promote aggregation. Chlorination resulted in additional inter- or intra -S-S- bond formation followed by a decrease in the total sulfhydryl group content. Amino groups were oxidised to carbonyl moieties with a concomitant acidic shift of pi. Formation of chlorotyrosine at the chlorination step was confirmed and its further H202-mediated transformation to bityrosine was demonstrated. It has also been confirmed that tryptophan, and not tyrosine, is the first target for chlorination. SDS/PAGE and HPLC profiles revealed that HOCiyOCl" chlorination promotes formation of aggregates stabilised by non covalent bonds. In conclusion, we suggest that a dramatic change in the OVA molecule structure begins when the molar excess of HOC1/OC1 is about 2 per one reactive group in OVA.
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