Theoretical study on the mechanism of low-energy dissociative electron attachment for uracil.

The lowest electronically adiabatic potential energy surface of the uracil anion has been theoretically investigated with density-functional theory methods in order to understand the mechanism of the N-H bond dissociation induced by low-energy electron attachment. We found that the BH&HLYP level can reasonably describe both the dipole-bound and valence anionic states in a balanced way. With this density-functional theory level, we have constructed two-dimensional potential energy surfaces as a function of appropriate internal coordinates and discuss the importance of electronic coupling between the dipole-bound and valence anion states in dissociative electron attachment of uracil. The transition state geometry for the electronic isomerization between the dipole-bound anion and the pi* valence anion was successfully optimized and the barrier height for this isomerization was found to be relatively low. It was found that the out-of-plane motion of H at the C6 position plays the most important role in this isomerization process. Reduced-dimensionality quantum wave packet calculations taking two active internal coordinates into account have also been performed to interpret the resonance structures observed in cross sections for the N-H dissociation channel at a qualitative level.

The PI3K-Akt pathway promotes microtubule stabilization in migrating fibroblasts.

Directed cell migration is controlled by extracellular cues such as growth factors/chemokines and extracellular matrix. In a migrating cell, a subset of microtubules becomes stabilized, and this stabilization is implicated in the establishment and maintenance of cell polarity. It is still not fully understood, however, how extracellular cues regulate the dynamics of microtubules. Here we show that the PI3K-Akt signaling pathway plays a pivotal role in growth factor regulation of microtubule stability. Treatment of NIH 3T3 fibroblasts with platelet-derived growth factor (PDGF) increases the amount of stabilized microtubules, and this increase is abrogated by the addition of a PI3K inhibitor or by expression of a dominant-negative form of Akt (DN-Akt), but not by the addition of a MEK inhibitor. Expression of an active form of Akt slightly increases the bulk amount of stabilized microtubules. Stabilization of microtubules induced in edge cells in the wounded monolayer culture is also attenuated by the PI3K inhibitor treatment or by expression of DN-Akt. Given that Akt is activated at the leading edge of a migrating cell and plays an essential role in directed cell migration, these results reveal a novel mechanism linking extracellular cues to directed cell migration, namely Akt regulation of microtubule stability.

A modified model for non-newtonian viscosity behavior of Aureobasidium pullulans culture fluid.

The culture fluid of the fungus Aureobasidium pullulans and the exopolysaccharide solution obtained by removal of the microbial cells exhibit a marked shear dependence of viscosity. The viscosity in a high shear rate region was a little higher than that predicted by a non-Newtonian viscosity equation derived previously on the basis of the concept of traveling force. In a sample exhibiting such high shear rate dependence, a hydrodynamic effect based on the fluid structure of the binding of contacting polymers and suspended microbial cells on viscosity becomes comparatively significant. A model for the shear rate dependence of the viscosity is needed to elucidate the mechanism of the viscosity behavior. A term concerning the increase in viscosity caused by the binding of polymers and the microbial cells suspended in a medium was added to the previous viscosity equation. The experimental shear dependence of the viscosity was well simulated by the modified viscosity equation.

Characteristic behavior of viscosity and viscoelasticity of Aureobasidium pullulans culture fluid.

Measurements of dynamic viscoelasticity and steady flow viscosity were made for culture fluids obtained by cultivation of Aureobasidium pullulans IAM 5060 with initial pHs of 6 and 7 and for exopolysaccharide (EPS) solutions obtained by removal of microbial cells. The molecular weight of EPS of the pH 6 culture is about 850,000, and that of the pH 7 culture is much larger. In the present study, the complex viscosity shifted to a considerably larger value than that of the steady flow viscosity. This differs from the Cox-Merz experience law which claims that there is a similarity between the angular frequency dependence of complex viscosity and the shear rate dependence of steady flow viscosity. On the other hand, the dynamic viscosity at small strain amplitude practically corresponded to the steady flow viscosity. The storage modulus of the pH 7 samples decreased markedly with a strain amplitude of more than 0.2, indicating that a dense network structure was formed. The linear region of the plot of viscoelasticity against strain amplitude was wider for the pH 6 culture, reflecting the stability of the network structure in this sample. The viscoelastic level of the EPS solution was a little greater than that of the culture fluid. This suggests that the viscoelasticity of the culture fluid is mainly caused by network structure forming among dissolved polysaccharides.