@techreport{oai:kanazawa-u.repo.nii.ac.jp:00011989,
 month = {Feb},
 note = {Human carbonic anhydrase II (HCA II) catalyses the reversible hydration of CO2. In this enzyme, the imidazole ring of histidine at position 64 (His64) functions to transfer the productive proton from the zinc-bound water to the buffer molecule in bulk-water. X-ray data of HCA II show that His64 has two types of side chain orientations, ”in” and ”out”, representing the direction of the imidazole ring toward and away from the active site, respectively. Maupin et al. reported that the imidazole of His64 can be rotated in a model system of the active site to clarify the proton transfer of catalytic mechanism. However, the indole ring of tryptophan at position 5 (Trp5) that is located near the ”out” of the imidazole ring of His64 was not considered in the model system. In this study, in order to estimate detailed rotational properties of His64, we constructed two His64-containing models with and without Trp5, and then simulate the constructed structures by using MP2 method and 6-311++G(d,p) basis sets. This allows us to tentatively determine the potential energies of the π-stacking interaction of the imidazole with the indole in relation to the side chain rotation of His64. The result indicates that the π-stacking interaction causes an increase of the energy barrier between ”in” and ”out” conformations, implying that the rotational motion of His64 is not relevant to explain the proton transfer during catalysis. Alternatively, a steady position of His64 would be needed in the proton transfer in catalytic mechanism of HCA II.},
 title = {Theoretical study of a π-stacking interaction in carbonic anhydrase},
 year = {2013}
}