Valinomycin is a macrocyclic ionophore that transports K + across hydrophobic membranes. Its function depends on selectivity, capture, transport, and release of the ion. While thermodynamics clearly indicate that valinomycin binds K + preferentially over all other alkali ions, characterizing the capture/transport/release of K + by valinomycin at the molecular level remains a challenge. The bracelet-like structure of valinomycin-K + (K + VM) has the ion completely enveloped, facilitating transport through the cell membrane. We report that hydration by a single water molecule, (K + VM)(H 2 O), produces three different conformers, identified by infrared spectroscopy and supporting computational studies. For two minor conformers, the water prevents the ionophore from closing, a conformation that would inhibit diffusion through the membrane. However, the dominant conformer encloses both the ion and the water, replicating the bracelet-like K + VM and arguably enhancing diffusion through the membrane. This potential for active participation of water in transport through the hydrophobic cellular membrane has never been previously considered.
Valinomycin (VM) is a natural K+-selective ionophore that transports K+ through the cell membrane. VM captures K+ in its central cavity with a C3-symmetric β-turn-like backbone. Although the binding affinity...
A CO2 laser polarimeter to measure the Faraday rotation in the large helical device (LHD) was developed and installed on a LHD. A CO2 laser whose wavelength is 10.6 μm was selected to avoid effects of the refraction. The Faraday rotation angle along toroidally tangential chords is of the order of one degree. The polarimeter utilizes the frequency-shift heterodyne technique with the use of acousto-optic modulators for high resolution. This polarimeter can be operated with a maximum of three channels. The accuracy of the Faraday rotation angle with a time resolution of 16 ms is about 0.01 deg by digital complex demodulation. We succeeded in performing preliminary measurements of the Faraday rotation angle from LHD plasmas and the values were 10%–30% larger than those estimated with the electron density profiles from interferometry.
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