The Effects of Nano-anatase TiO2 on the Activation of Lactate Dehydrogenase from Rat Heart

Lactate dehydrogenase (LDH, EC1.1.1.27), widely expressed in the heart, liver, and other tissues, plays an important role in glycolysis and glyconeogenesis. The activity of LDH is often altered upon inflammatory responses in animals. Nano-TiO2 was shown to provoke various inflammatory responses both in rats and mice; however, the molecular mechanism by which TiO2 exerts its toxicity has not been completely understood. In this report, we investigated the mechanisms of nano-anatase TiO2 (5 nm) on LDH activity in vitro. Our results showed that LDH activity was greatly increased by low concentration of nano-anatase TiO2, while it was decreased by high concentration of nano-anatase TiO2. The spectroscopic assays revealed that the nano-anatase TiO2 particles were directly bound to LDH with mole ratio of [nano-anatase TiO2] to [LDH] was 0.12, indicating that each Ti atom was coordinated with five oxygen/nitrogen atoms and a sulfur atoms of amino acid residues with the Ti-O(N) and Ti-S bond lengths of 1.79 and 2.41 angstrom. We postulated that the bound nano-anatase TiO2 altered the secondary structure of LDH, created a new metal ion-active site for LDH, and thereby enhanced LDH activity.