65 research outputs found
Caracterização do cruzamento entre as raças suÃnas landrace x large White x moura pra formação de hÃbridos da linha fêmea.
A solid film electrode of intermetallic Ag2Hg3.02 for the direct determination of folic acid in fresh and processed fruit juices.
Polyamine Sharing between Tubulin Dimers Favours Microtubule Nucleation and Elongation via Facilitated Diffusion
We suggest for the first time that the action of multivalent cations on
microtubule dynamics can result from facilitated diffusion of GTP-tubulin to the
microtubule ends. Facilitated diffusion can promote microtubule assembly,
because, upon encountering a growing nucleus or the microtubule wall, random
GTP-tubulin sliding on their surfaces will increase the probability of
association to the target sites (nucleation sites or MT ends).
This is an original explanation for understanding the apparent discrepancy
between the high rate of microtubule elongation and the low rate of tubulin
association at the microtubule ends in the viscous cytoplasm. The mechanism of
facilitated diffusion requires an attraction force between two tubulins, which
can result from the sharing of multivalent counterions. Natural polyamines
(putrescine, spermidine, and spermine) are present in all
living cells and are potent agents to trigger tubulin self-attraction. By using
an analytical model, we analyze the implication of facilitated diffusion
mediated by polyamines on nucleation and elongation of microtubules. In
vitro experiments using pure tubulin indicate that the promotion of
microtubule assembly by polyamines is typical of facilitated diffusion. The
results presented here show that polyamines can be of particular importance for
the regulation of the microtubule network in vivo and provide
the basis for further investigations into the effects of facilitated diffusion
on cytoskeleton dynamics
Ion exchange and DNA molecular dip sticks: studying the nanoscale surface wetting of muscovite mica
Mica is an abundant crystal mineral that has important and interesting bulk and surface properties for a variety of applications. These properties arise from its anisotropic structure, in which layers of aluminum silicate, 1 nm thick, are ionically bonded together, typically with K+ ions. The surface properties of mica can be varied through ion exchange with the exposed lattice sites. In this study, the effect of kinetics on ion exchange with nickel ions (Ni2+) and its influence on surface water accumulation as a function of time has been investigated. Mica was ion-exchanged for 30 s or 5 min for a range of Ni2+ concentrations (i.e., 1.0-20.0 mM), and its surface properties were measured for up to 96 h after incubation in a controlled environment. The nanoscale physicochemical properties of nickel-functionalized muscovite mica (Ni-mica) were investigated by reconstructing the conservative force profile between an atomic force microscopy (AFM) tip and the surface. This information provides a hint of the surface water accumulation and enables details of the spatial and temporal variations in surface properties due to the ion-mediated adsorption of water to be elucidated. Variations in the water-layer accumulation were confirmed using noncontact AFM imaging under ambient conditions and DNA molecules as "molecular dip sticks". It was found that the surface properties were largely independent of the incubating concentration but did depend on the incubation time during ion exchange and the aging time. For the longer incubation time of 5 min, the water-layer accumulation remained constant at around ∼1.5 nm deep, whereas for the short incubation time of 30 s, the accumulation was initially subnanometer but grew with aging time and converged to a similar final value after 96 h. The extracted force of adhesion (FAD) also showed the same trends, where reduced values of FAD indicated increased screening of the van der Waals interaction through thicker water layers
Strength gain through eccentric isotonic training without changes in clinical signs or blood markers
Localized Nanoscopic Surface Measurements of Nickel-Modified Mica for Single-Molecule DNA Sequence Sampling
- …