Conformational change of H+-ATPase beta monomer revealed on segmental isotope labeling NMR spectroscopy

F1-ATPase has been shown to be a stepwise molecular motor. Its rotation mechanism has been explained by the interaction of the gamma axis with the open and closed forms of the beta subunit. Although NMR should be a powerful method for elucidating its mechanism, its molecular size (473 amino acid residues, 52 kDa) is a major obstacle. We have applied segmental labeling based on intein ligation to the beta subunit, and succeeded in assigning 89% of the NH (402/451), 89% of the Calpha (417/473), 83% of the Cbeta (357/431), and 90% of the CO (425/473) signals of the beta subunit monomer. The secondary structures predicted from the chemical shifts of the main chain atoms and the relative orientations determined from residual dipolar couplings indicated that the subunit beta monomer takes on the open form in the absence of nucleotide. Furthermore, the chemical shift perturbation and the residual-dipolar-coupling changes induced by nucleotide binding show that conformational change from the open to the closed form takes place on nucleotide binding. The intrinsic conformational change of the beta subunit monomer induced by nucleotide binding must be one of the essential driving forces for the rotation of F1-ATPase.     

Direct measurement of the parapositronium lifetime in alpha-SiO2

The mean lifetime of delocalized parapositronium in alpha-SiO2 has been determined directly for the first time using a newly developed positron lifetime spectrometer based on BaF2 scintillators and a fast digital oscilloscope. The lifetime is found to be 156+/-4 ps, which is much longer than its intrinsic lifetime of 125 ps. This indicates clearly that the primary many-body effect on positronium in alpha-SiO2 is the screening of the Coulomb interaction between the constituent particles by electrons of the medium and that the average distance between the electron and positron in positronium becomes larger than its vacuum value.     

Nonlinear features and response mechanisms of a PtO2 mask layer for optical data storage with a superresolution near-field structure

Optical features of a PtO2 mask layer in a superresolution near-field structure are investigated in detail by use of the Z-scan technique. The high photothermal stability of the PtO2 mask is revealed, and a phenomenon in which laser-irradiated PtO2 decomposes to yield Pt particles is confirmed. We also find a physical change in the mask layer that accompanies the chemical decomposition. Microscopic observations and atomic force microscope studies support the theory that the physical deformation is induced by the decomposition of PtO2. It is clear that the optical nonlinear responses of the PtO2 mask layer result from two mechanisms.     

Constructing self-organized structures on silicon and sapphire surfaces

We investigated methods to fabricate distinctive structures on silicon and sapphire substrates to grow a carbon nanotube (CNT) network using a solution from the Belousov-Zhabotinsky (BZ) reaction. The BZ reaction is a chemical system where chemical reactions and material diffusion coexist in a nonequilibrium state and generate spatiotemporal patterns in a petri dish. Precipitates from the reaction should also produce distinctive structures after being piled on the substrates. The structures have metal particles that act as catalysts for growing CNTs or quantum dots of nanodot devices. Therefore, such structures should be suitable to fabricate three-dimensional CNT networks or nanodot devices. To confirm this, we investigated the fabrication of distinctive structure using a BZ reaction solution. Results indicated that the BZ reaction solution produced interesting structures on the substrates. Moreover, we confirmed that the shape of the structure changed when the substrate used was changed. We believe that the developed methods are suitable to fabricate nanodevices, especially CNT network devices.