Inhibition of Lysozyme by Taurine Dibromamine

M.   S.   Petronio; V.   F.   Ximenes

Abstract

Hypobromous acid (HOBr) is a powerful oxidant produced by stimulated neutrophils and eosinophils. Taurine, a non-protein amino acid present in high amounts in the leukocytes, reacts instantaneously with HOBr leading to their haloamine derivative taurine dibromamine (Tau-NBr₂). Lysozyme is a bactericidal enzyme also present in leukocytes and in secretory fluids. The inhibition of lysozyme is a pathway for bacterial proliferation in inflammatory sites. Here, we investigated the inhibition of the enzymatic activity of lysozyme when it was submitted to oxidation by Tau-NBr₂. We found that the oxidation of lysozyme by Tau-NBr₂ decreased its enzymatic activity in 80%, which was significant higher compared to the effect of its precursor HOBr (30%). The study and comparison of Tau-NBr₂ and HOBr regarding the alterations provoked in the intrinsic fluorescence, synchronous fluorescence, resonance light scattering and near and far-UV circular dichroism spectra of lysozyme and oxidized lysozyme revealed that tryptophan residues in the active site of the protein were the main target for Tau-NBr₂ and could explain its efficacy as inhibitor of lysozyme enzymatic activity. This property of Tau-NBr₂ may have pathological significance, since it can be easily produced in the inflammatory sites.

Keywords: Eosinophils, hypobromous acid, hypochlorous acid, lysozyme, neutrophils, taurine dibromamine.

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