応用物理学会春季・秋季学術講演会

Here, we report results of our study on the mechanism of spin-dependent O₂ reaction with hemoglobin. O₂ reaction with hemoglobin, which we represent as FePIm (Fe = iron, P = porphyrin, Im = imidazole), involves the transition between two spin-dependent states, viz., the oxyhemoglobin state and the deoxyhemoglobin state. The deoxyhemoglobin state pertains to FePIm and a free O₂, while the oxyhemoglobin state pertains to an O₂ bound to FePIm. The deoxyhemoglobin and oxyhemoglobin systems have triplet and singlet total magnetizations, respectively. We found that a spin transition from triplet to quintet to singlet mediates the O₂ binding process, and this accelerates the reaction. We also found that the position of the Fe atom out of the porphyrin plane is an important indicator of O₂ affinity. These results indicate that spin transitions/crossings affect the activation energy barrier. Further details will be discussed at the meeting.