Low frequency ultrasound induces aggregation of porcine fumarase by free radicals production.

Hydrogen peroxide and hydroxyl-free radicals determine a diffuse aggregation of porcine fumarase and a loss of its enzymatic activity. In this study, hydroxyl-free radicals were generated "in situ" by irradiation with ultrasound (US) at 38 kHz. The structural characteristics of aggregated fumarase were studied using circular dichroism spectroscopy (CD) and steady state fluorescence spectroscopy. Enzyme aggregation is caused by the formation of intermolecular disufide bridges, originated by the oxidation of cysteine residues, together with a diffuse increase in beta-turn in the protein's secondary structure. These conformational changes lead to a fibrous, amyloid-like aggregation which appears ordered and regular under TEM microscopy.