Quantification of short term signaling by the epidermal growth factor receptor.

During the past decade, our knowledge of molecular mechanisms involved in growth factor signaling has proliferated almost explosively. However, the kinetics and control of information transfer through signaling networks remain poorly understood. This paper combines experimental kinetic analysis and computational modeling of the short term pattern of cellular responses to epidermal growth factor (EGF) in isolated hepatocytes. The experimental data show transient tyrosine phosphorylation of the EGF receptor (EGFR) and transient or sustained response patterns in multiple signaling proteins targeted by EGFR. Transient responses exhibit pronounced maxima, reached within 15-30 s of EGF stimulation and followed by a decline to relatively low (quasi-steady-state) levels. In contrast to earlier suggestions, we demonstrate that the experimentally observed transients can be accounted for without requiring receptor-mediated activation of specific tyrosine phosphatases, following EGF stimulation. The kinetic model predicts how the cellular response is controlled by the relative levels and activity states of signaling proteins and under what conditions activation patterns are transient or sustained. EGFR signaling patterns appear to be robust with respect to variations in many elemental rate constants within the range of experimentally measured values. On the other hand, we specify which changes in the kinetic scheme, rate constants, and total amounts of molecular factors involved are incompatible with the experimentally observed kinetics of signal transfer. Quantitation of signaling network responses to growth factors allows us to assess how cells process information controlling their growth and differentiation.     

Control of molecular transformations in polyenzyme systems: quantitative theory of the regulation of metabolism

An attempt of a comprehensive treatment of the theory of metabolic control is presented. The introductory section giving an outline of the early development of the theory, is followed by definitions quantifying the control in the metabolic system. By means of the perturbation method the complete system of equations is obtained which allows one to express all the enzyme control coefficients ("global" coefficients) through the elasticity coefficients characterizing kinetic properties of individual enzymes ("local" coefficients) and through the steady-state values of metabolic fluxes and concentrations. It is shown how connectivity relations between global and local coefficients should be modified when conserved sums of intermediates are present in the system. A new theorem is derived, it allows one to express the global response of the system to any change in the external parameter (such as external effector concentration, or temperature, pH, ionic strength, ets.) through the control coefficients and local responses of individual reaction steps. Explicit formulas are derived for response coefficients of the fluxes and concentrations to changes in the conserved sums of intermediates, which express the values of these global coefficients through the control and elasticity coefficients of enzymes and steady-state pools. The results obtained comprise as a special case all the results published so far in the literature.     

Plant virus infection development as affected by heavy metal stress

The work was focused on the investigation of possible dependencies between the development of viral infection in plants and the presence of high heavy metal concentrations in soil. Field experiments have been conducted in order to study the development of systemic tobacco mosaic virus (TMV) infection in Lycopersicon esculentum L. cv. Miliana plants under effect of separate salts of heavy metals Cu, Zn and Pb deposited in soil. As it is shown, simultaneous effect of viral infection and heavy metals in tenfold maximum permissible concentration leads to decrease of total chlorophyll content in experiment plants mainly due to the degradation of chlorophyll a. The reduction of chlorophyll concentration under the combined influence of both stress factors was more serious comparing to the separate effect of every single factor. Plants' treatment with toxic concentrations of lead and zinc leaded to slight delay in the development of systemic TMV infection together with more than twofold increase of virus content in plants that may be an evidence of synergism between these heavy metal's and virus' effects. Contrary, copper although decreased total chlorophyll content but showed protective properties and significantly reduced amount of virus in plants.     

Phenotype characteristic of the ionomycin-resistant CD4+ subset of the peripheral blood T-lymphocytes

The differential sensitivity of peripheral blood (PB) CD4+ T lymphocytes to the calcium ionophore ionomycin was investigated. Effect of ionomycin exerted on T cells was time- and dose-dependent. We have shown that resistant cells belonged to some distinct T cell subsets. The resting naive CD4+CD45RA+ T cells showed a little, if any, resistance to ionomycin treatment. The primed CD4+CD45R0+ memory T cells behaved similarly as did ionomycin-resistant (IR) cells. Although IR CD4+ T cells had a typical "memory" phenotype, some quantitative differences were found in expression of CD11a, CD28, CD29, CD62L and CD243 markers between PB CD4+CD45R0+ T cells and corresponding IR cells.     

Cellular information transfer regarded from a stoichiometry and control analysis perspective

Metabolic control analysis (MCA) allows one to formalize important aspects of information processing in living cells. For example, information processing via multi-level enzyme cascades can be quantified in terms of the response coefficient of a cellular target to a signal. In many situations, control and response coefficients cannot be determined exactly for all enzymes involved, owing to difficulties in 'observing' all enzymes experimentally. Here, we review a number of qualitative approaches that were developed to cope with such situations. The usefulness of the concept of null-space of the stoichiometry matrix for analysing the structure of intracellular signaling networks is discussed. It is shown that signal transduction operates very efficiently when the network structure is such that the null-space matrix can be block-diagonalized (which may or may not imply that the network consists of several disconnected parts) and some enzymes have low elasticities to their substrates.     

Initial stages of steel biocorrosion

Initial stages of corrosion of mild steel induced by Klebsiela rhinoscleromatis BO2 were studied in various media. The effect of the microorganism was detected 8-10 h after inoculation. The number of viable cells were virtually unchanged within one month in all media, but the corrosive activity of the strain decreased. The corrosive activity of microorganisms can be determined by spectrophotometry even only after incubation for 24 h. At a low level of organic substrate, even strong colonization with microorganisms does not inevitably result in a significant damage to metals.     

Chemical-microbiological diagnosis of stress-corrosive damage to pipelines]

Samples of soil, ground, electrolyte, corrosion products, and protective coating were taken after excavating pipelines. The depth of stress corrosion cracks of the pipe steel was mostly related to the numbers of sulfate-reducing and denitrifying bacteria. In certain types of soil, damage correlated with the number of acid-producing microorganisms and aerobic chemoorganotrophs (saprophytes). A correlation was found between the extent of stress-corrosion damage to pipelines and the contents of reduced iron, sulfides, and organic carbon in surrounding ground.     

Effect of space flight conditions on properties of hydrocarbon-oxidizing bacteria

Results of experiments on the Mir space station (EO-25 and EO-26) demonstrated that the conditions of orbital flight, primarily the cosmic radiation, was a mutagenic factor affecting both the genotype and phenotype of an oil-oxidizing bacterial strain, Mycobacterium flavescens EX-91. The emerging mutants differed from original culture by the rate of colony growth and the ability to ferment certain carbohydrates or synthesize beta-galactosidase. Changes in the rate of utilization of raw oil and individual hydrocarbon types (constituting model mixtures) suggest that cosmic radiation may serve as a means of obtaining mutant clones of microorganisms with new properties.     

Study of the integral toxicity of aqueous media, polluted by petroleum and petroleum products using bacterial tests

A biotest kit was used to assess the integral toxicity level of aquatic medium contamination with petroleum and petroleum-based products. The integral toxicity dynamics was also monitored during biodegradation of petroleum and petroleum-based products by an association of petroleum-degrading strains including Acinetobacter sp., Mycobacterium flavescens, and Rhodococcus sp. The following bacterial tests were used: the bioluminescence (BL) test based on Photobacterium leiognathi; electro-orientation (EO), optoosmotic (OO), and growth test; as well as the reducing activity (RA) test based on the Agrobacterium radiobacter culture. No significant increase in the integral toxicity level of aquatic medium was observed when diesel fuel and kerosene contamination had been subjected to biodegradation. Although express biotests (EO, OO, RA, and BL) detected a pronounced increase in the integral toxicity of aquatic medium, long-term growth biotest revealed no statistically significant increase in the toxicity level.