Lysozyme Dimer Formation on Lysozyme Oxidation with as Studied by Fluorescence Evolution

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Abstract
Lysozyme dimers produced on oxidation of lysozyme with in aqueous solutions exhibit a fluorescence spectrum (λmax=400 nm) closely similar to that of bi-tyrosine. This suggests that the dimer is likely to have a tyrosin–tyrosine bond resulting from the combination of tyrosine phenoxy radicals of two lysozyme molecules. Kinetic studies on dimer formation were made by measuring time-dependent fluorescence after pulsed-electron irradiation over wide pH range. The results lead to the following conclusions. The second-order growth of the dimer fluorescence observed at pH 10·7–12·5 reflects the combination process of the lysozyme radicals, which is rate-determining in the pH range. On the other hand, the first-order growth observed at pH 6·8–10·2 is attributable to the enolization of the keto-form of the dimer. A tentative reaction scheme is proposed for the dimer formation.