Toxic interaction mechanism between oxytetracycline and bovine hemoglobin

Oxytetracycline (OTC) is a kind of widely used veterinary drugs. The residue of OTC in the environment is potentially harmful. In the present work, the interaction between OTC and bovine hemoglobin (BHb) was investigated by fluorescence, synchronous fluorescence, UV-vis absorption, circular dichroism and molecular modeling techniques under physiological conditions. The experimental results showed that OTC can bind with BHb to form complex. The binding process is a spontaneous molecular interaction procedure, in which van der Waals and hydrogen bonds interaction play a major role. The number of binding sites were calculated to be 1.12 (296K), 1.07 (301K) and 0.95 (308K), and the binding constants were of K_296K=9.43×10⁴Lmol^-1, K_301K=4.56×10⁴Lmol^-1 and K_308K=1.12×10⁴Lmol^-1 at three different temperatures. Based on the Förster theory of nonradiative energy transfer, the binding distance between OTC and the inner tryptophan residues of BHb was determined to be 2.37nm. The results of UV-vis absorption, synchronous fluorescence and CD spectra indicated that OTC can lead to conformational and some microenvironmental changes of BHb, which may affect physiological functions of hemoglobin. The synchronous fluorescence experiment revealed that OTC binds into hemoglobin central cavity, which was verified by molecular modeling study. The work is helpful for clarifying the molecular toxic mechanism of OTC in vivo.