Effect of Terahertz Radiation on the Strength of Binding in Albumin Complexes with Nitrogen Oxide and Oxygen
The influence of terahertz radiation on the transport characteristics of serum albumin manifests itself as changes in bonding with biologically significant species, such as molecular oxygen and nitrogen oxide. Causing no rupture of covalent bonds, terahertz radiation may affect rotational and rovibrational transitions in biomolecules. To observe the effects of this kind, it is necessary to study their chemical consequences. One of these consequences is a change in the transport characteristics of albumin, namely strengthening or weakening of protein bonding with the species to be transported, in particular O2 and NO. These changes were successfully followed with the help of in situ spin probing and spin trapping. We demonstrate that irradiation within the terahertz range has a noticeable effect not only on the amount of specific adsorption centers in albumin molecule but also affects the affinity of these centers. After irradiation, albumin binds oxygen to a higher extent than the non-irradiated preparation. This was concluded because we observed an increase in the intensity of the EPR signal of the nitroxide, a spin probe which was formed directly in the system through the oxidation of the precursor nitrone molecule at the paramagnetic centers of albumin. In addition, irradiation resulted in a decrease in the mobility of these paramagnetic centers, which was observed as an increase in the width of EPR signals in the spectrum of the sample under investigation. The interaction of preliminarily irradiated albumin with NO caused stronger local acidification than the interaction of non-irradiated albumin, Acidification was measured with the help of a pH-sensitive imidazoline spin trap. This allows us to conclude that NO NO2 conversion proceeds at a higher rate in the presence of irradiated albumin, which means that the albumin – NO complex becomes weaker after irradiation. Further studies are necessary to identify the rotational transitions responsible for the observed effects. As the initial step, we carried out the simulation of the interaction of oxygen and nitrogen oxide with the functional groups of albumin molecule. The changes in bond strength in the studies complexes may be due to a conformational rearrangement in the proline-containing fragment. This agrees with the known facts that the terahertz radiation affects the ternary structure in which a special role is played by the proline fragment.