Estudos biofísicos da interação do timerosal, um composto orgânico de mercúrio, com a catalase.

Abstract

Catalase (CAT) is an antioxidant enzyme that acts in the defense system, protecting cells from toxic effects. The interaction of this enzyme with any external chemical species may influence its catalytic activity in vivo, bringing about different effects, such as oxidative stress. Among these species, mercury stands out, whose human toxicity varies according to chemical form, dose and exposure, being associated with a series of diseases, including in the central nervous system and psychic functions. Thus, the present study sought to evaluate the interaction between CAT and thimerosal (TM), an organic mercury compound used as a preservative mainly in vaccines, aiming to investigate possible changes in this enzyme and, therefore, changes in the performance of its physiological functions . This study was monitored by spectroscopic techniques evaluating different parameters and in vivo tests. The interaction process was monitored due to the decay of the intrinsic fluorescence of the catalase after the addition of TM to the medium, due to the formation of the non-fluorescent supramolecular complex, with the type of static quenching. The interaction process was spontaneous (∆G <0) and the preferred interaction forces are the Van der Waals forces and hydrogen bonds (∆H <0 and ∆S <0), with a portion of electrostatic forces involved. The stoichiometry of the complex formed was 1: 1 (n ~ 1), with Kb values indicating an interaction force of the order of 104. Structural, hydrophobicity changes and around the tryptophan and tyrosine residues of the protein were evidenced by 3D fluorescence, ANS assay and synchronized fluorescence respectively, indicating that there were changes in the secondary structure, preferably in the tryptophan residues. The influence of different species, some present in the plasma, during the interaction was also evaluated. As well as the influence of changes arising from the interaction with TM on CAT activity, through enzymatic studies, verifying a reduction of about 85% in the action of this enzyme, indicating the influence of TM on the decomposition of H2O2, in agreement with the value of IC50 (14.75 µM), due to the mixed inhibition mechanism, being a more effective inhibitor than Hg (II). And according to in vivo tests, TM causes high lethality in drosophilas, altering the activity of CAT in males of this species and can be considered teratogenic due to the changes caused in Zebrafish. Therefore, these results can assist in the understanding of possible effects related to the disorder caused by thimerosal in biological systems, in particular the effects when associated with catalase.