Deviations from hyperbolic kinetics in slowly dissociating allosteric enzyme systems]

The feautres of kinetic behavior of dissociating enzyme systems for which the rate of equilibrium between the oligomeric forms is slow in comparison with the rate of the enzymatic process are discussed. It is shown that in slowly dissociating enzyme system of the type Np in equilibrium P (P is the enzyme oligomer, and p is the subunit: N greater than or equal to2) in which P and p forms differ by the character of allosteric interaction between the active and allosteric sites the plots of the initial reaction rate (v) versus substrate (S) or effector (F) concentration may be a very complicated shape. In similar systems the v versus [S]0 plots may have intermediate plateau, maximum and minimum simultaneously, sigmoidality followed by intermediate plateau and so on, and the v versus [F]0 plots may have intermediate plateau.     

Abelson interactor protein-1 positively regulates breast cancer cell proliferation, migration, and invasion

Abelson interactor protein-1 (ABI-1) is an adaptor protein involved in actin reorganization and lamellipodia formation. It forms a macromolecular complex containing Hspc300/WASP family verprolin-homologous proteins 2/ABI-1/nucleosome assembly protein 1/PIR121 or Abl/ABI-1/WASP family verprolin-homologous proteins 2 in response to Rho family-dependent stimuli. Due to its role in cell mobility, we hypothesized that ABI-1 has a role in invasion and metastasis. In the present study, we found that weakly invasive breast cancer cell lines (MCF-7, T47D, MDA-MB-468, SKBR3, and CAMA1) express lower levels of ABI-1 compared with highly invasive breast cancer cell lines (MDA-MB-231, MDA-MB-157, BT549, and Hs578T), which exhibit high ABI-1 levels. Using RNA interference, ABI-1 was stably down-regulated in MDA-MB-231, which resulted in decreased cell proliferation and anchorage-dependent colony formation and abrogation of lamellipodia formation on fibronectin. Down-regulation of ABI-1 decreased invasiveness and migration ability and decreased adhesion on collagen IV and actin polymerization in MDA-MB-231 cells. Additionally, compared with control parental cells, ABI-1 small interfering RNA-transfected cells showed decreased levels of phospho-PDK1, phospho-Raf, phospho-AKT, total AKT, and AKT1. These data suggest that ABI-1 plays an important role in the spread of breast cancer and that this role may be mediated via the phosphatidylinositol 3-kinase pathway.     

Self-similarity in variability of human heart variability at various stages of ontogenesis

We consider the potential of applying wavelet analysis to fluctuations found in physiological systems. We focus on cardiac interbeat interval time series (RR-intervals) from a group of young adults and children and fetus heart beat rate time series (antepartum cardiotocography), because the wavelet analysis of these heart rate dynamics may provide important practical diagnostic and prognostic information not obtainable with current approaches. We show that all the signals analyzed are self-similar and propose a method for estimating this scaling feature.     

Hepatocyte dynamic reserve: the mechanism for the assurance of specialized functions in the regenerating liver]

A short review is presented of the experimental data on the interrelation between specialized functions and proliferative activity of cells in regenerating mammalian liver. Using the results of the kinetic analysis of induced cell proliferation makes it possible to elicit an existence of the dynamic redistribution of hepatocytes between "the reserve" of quiscent cells (in respect to the mitotic cycle) and the population of actively proliferating cells. This fenomen referred to as "the dynamic reserving of cells" is considered in this work as a possible mechanism of maintenance of the specialized functions of the liver during its regeneration after a partial hepatectomy.     

Extracellular ribonuclease from Bacillus pumilus]

The extracellular ribonuclease (RNAse Bp) was isolated from the cultural medium filtrate of Bacillus pumilus by ammonium sulfate precipitation and two stages of ion-exchange chromatography on carboxymethyl- and phospho-cellulose columns. The amino acid composition and N-terminal amino acid residue have been determined. The kinetic parameters of cleavage reaction of synthetic polynucleotides have been measured. According to their structural homology RNAse Bp has been shown to be similar to RNAses Ba and Bi. Catalytic properties of the enzyme are very close to RNAse Bi.