Energetic Mechanism of Cytochrome c-Cytochrome c Oxidase Electron Transfer Complex Formation under Turnover Conditions Revealed by Mutational Effects and Docking Simulation

Based on the mutational effects on the steady-state kinetics of the electron transfer reaction and our NMR analysis of the interaction site (Sakamoto, K., Kamiya, M., Imai, M., Shinzawa-Itoh, K., Uchida, T., Kawano, K., Yoshikawa, S., and Ishimori, K. (2011) Proc. Natl. Acad. Sci. U.S.A. 108, 1227112276), we determined the structure of the electron transfer complex between cytochrome c (Cyt c) and cytochrome c oxidase (CcO) under turnover conditions and energetically characterized the interactions essential for complex formation. The complex structures predicted by the protein docking simulation were computationally selected and validated by the experimental kinetic data for mutant Cyt c in the electron transfer reaction to CcO. The interaction analysis using the selected Cyt c-CcO complex structure revealed the electrostatic and hydrophobic contributions of each amino acid residue to the free energy required for complex formation. Several charged residues showed large unfavorable (desolvation) electrostatic interactions that were almost cancelled out by large favorable (Columbic) electrostatic interactions but resulted in the destabilization of the complex. The residual destabilizing free energy is compensated by the van der Waals interactions mediated by hydrophobic amino acid residues to give the stabilized complex. Thus, hydrophobic interactions are the primary factors that promote complex formation between Cyt c and CcO under turnover conditions, whereas the change in the electrostatic destabilization free energy provides the variance of the binding free energy in the mutants. The distribution of favorable and unfavorable electrostatic interactions in the interaction site determines the orientation of the binding of Cyt c on CcO

MEASUREMENT OF WAVY SURFACE OSCILLATIONS ON LIQUID METAL LITHIUM JET FOR IFMIF TARGET

ABSTRACT This paper reports on the measurement of surface waves on a liquid lithium jet and results of the study of the Li target at the International Fusion Materials Irradiation Facility (IFMIF). The characteristics of the surface waves at the nozzle exit and just downstream of it were examined experimentally, since the initial growth of free surface waves exerts a definite influence on surface behavior in the downstream region. Experiments were carried out using the lithium circulation loop at Osaka University, with a focus on the free surface oscillations. These oscillations were measured using an electrocontact probe apparatus, which detects electric contacts between the probe tip and the Li surface. The apparatus was installed 15 mm downstream from the nozzle exit and was scanned along the liquid-depth direction. The contact signal recorded in the experiment was analyzed, and the wave amplitude and frequency of the surface waves were examined