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Equilibrium conformational fluctuation of Zn-substituted myoglobin (ZnMb) has been studied in the nanosecond to millisecond time region and 180-300 K temperature region by the time-resolved transient hole-burning spectroscopy. In this technique, the conformational fluctuation of the protein is observed as the temporal variation of the hole spectrum burned by irradiation of the laser pulse. ZnMb solution samples in various solvent conditions were prepared and investigated to elucidate the solvent effect on the conformational dynamics of Mb. The configuration coordinate model assuming the harmonic energy landscape has given a fairly good description of the time dependence of the hole spectra. The observed temporal behavior of both the hole shift and the hole broadening was well expressed by the same stretched exponential correlation function with a rather small and almost temperature-independent beta of 0.26. It was found that the correlation time tauc of the conformational fluctuation of ZnMb determined by this analysis depends linearly on the solvent viscosity regardless of the solvent composition and temperature. This means the almost 0 activation energy for the fluctuation process and can not be understood by simply assuming the Arrhenius-type crossing of the barriers separating the conformational substates. It is shown that this linear viscosity dependence of tauc, as well as the temperature-independent beta, is qualitatively explained in the framework of the hierarchically constrained dynamics (HCD) model [Palmer, R. G. et al. (1984) Phys. Rev. Lett. 53, 958-961] with the postulate that the dynamics in the lowest level in the HCD model corresponds in the actual system to the configuration fluctuations of the solvent molecules surrounding the protein.

Nanosecond to millisecond conformational fluctuations of Zn-substituted cytochrome c (ZnCytc) have been studied by the time-resolved transient hole-burning method. The investigation of low-temperature dynamics has been made on the ZnCytc solution sample in a water-glycerol mixture. The conformational fluctuations in the native-like and the molten-globule (MG)-like states have been compared for the aqueous solution samples at room temperature. ZnCytc in the MG-like state has been prepared by adding 200 mM NaClO4 to the protein solution with a pH of 2.1, and the formation of the MG-like state has been confirmed by both the far-UV CD and the visible absorption spectra. The hole spectrum of ZnCytc has been found to consist of two nearly degenerate components, that is, the Qx and Qy bands. The temporal change in the Qx component hole spectrum has been extracted by fitting the observed hole spectrum to the three-Gaussian form. The experimental results for ZnCytc dissolved in a water-glycerol mixture have revealed that the conformational fluctuation of ZnCytc is suppressed around 200 K, which is nearly the same temperature as the glass-like transition point of Zn-substituted myoglobin (ZnMb) and also as the glass-transition point of the solvent. This supports the idea of the solvent-induced glass-like transition of a protein. It has been also found that at physiological temperatures the time scale of the conformational fluctuation of ZnCytc lies around a few tens of nanoseconds, which is 2-3 orders of magnitude faster than that of ZnMb. The experimental results for the aqueous solution samples have shown that the difference between the native-like and the MG-like states is not conspicuous. However, they are indicative of the appearance of the slower conformational fluctuation in the MG-like state.

ESR dosimetry of some construction materials at Hiroshima and Nagasaki was carried out to determine the A-bomb radiation dose. Some minerals exposed to low-level natural radiation over a given geological time period can be also used to determine the intense A-bomb radiation dose. Finally, an ESR cavity and a special NdBFe (Neomax) magnet system for in-vivo measurement of radiation dose of a human tooth without extraction is designed and manufactured.