Manyetik alanın photolyase ve flavin içeren çözeltilerdeki etkisinin floresan tabanlı tespit edilmesi

It has been known that bird's navigation mechanism relies on the geomagnetic fi eld; however, the primary sensor is still a matter of debate. One of the leading hypotheses is based on the magnetic sensitivity of the radical pairs. According to this model, inside the photoactivated proteins such as cryptochrome and photolyase, flavin-tryptophan radical pairs are formed by photon absorption and electron transfer, and they can undergo coherent singlet-triplet interconversion which is affected by an external magnetic field. Absorption spectroscopy has been predominantly employed to monitor such magnetic field effects. This technique requires relatively high sample concentrations. Moreover, magnetic field sensitivity of individual molecules with different orientations is lost and only an average magnetoreception behavior can be observed. Recently, fluorescence-based approach has emerged as an alternative experimental strategy which is generally easier to perform and more sensitive. Despite this, up to now fluorescence-based experiments only revealed the magnetic fi eld effect in solutions containing flavin and tryptophan, but not actual photoactivated proteins. In this thesis, the magnetic fi eld effect on flavin containing solutions and photolyases is detected by utilizing fluorescence-based experiments. In the presence of around 28 mT magnetic fi eld, up to -5.55% magnetic field effect is observed for the solution of 1 µM flavin adenine dinucleotide (FAD) and 300 µM Trp. The roles of laser intensity, pH of the buffer, and magnetic fi eld strength in the magnetic fi eld sensitivity are investigated for the FAD and Trp containing solutions. The fluorescence based experiments are also conducted with photolyases. -1.34% and -1.01% magnetic field effects are measured for the solutions of 170 µM Vibrio cholera photolyase (VcPHR) and 166 µM Escherichia coli photolyase (EcPHR) respectively. Moreover, simulations to understand quantum coherence in the radical pair mechanism are performed, and the fluorescence based observation of coherent interconversion is discussed. Finally, we suggest conjugating the photoexcited proteins or flavin with dye molecules which serve as acceptors in Förster resonance energy transfer (FRET). In this method, the decay rate of the singlet and triplet states is further enhanced, revealing higher sensitivity of magnetic fi eld effect.