Use of the flux model of amino acid metabolism of Escherichia coli.

A program implementing a flux model of Escherichia coli metabolism was used to analyze the effects of the addition of amino acids (tryptophan, tyrosine, phenylalanine, leucine, isoleucine, valine, histidine, lysine, threonine, cysteine, methionine, arginine, proline) to minimal medium or media lacking nitrogen, carbon, or both. The overall response of the metabolic system to the addition of various amino acids to the minimal medium is similar. Glycolysis and the synthesis of pyruvate with its subsequent degradation to acetate via acetyl-CoA become more efficient, whereas the fluxes through the pentose phosphate pathway and the TCA cycle decrease. If amino acids are used as the sole source of carbon, nitrogen, or both, the changes in the flux distribution are determined mainly by the carbon limitation. The phosphoenolpyruvate to glucose-6-phosphate flux increases; the flux through the pentose phosphate path is directed towards ribulose-5-phosphate. Other changes are determined by the compounds that are the primary products of catabolism of the added amino acid.

[Model of genes expression regulation in bacteria by means of formation of secondary RNA structures].

In this article a model, first, classical attenuation RNA regulation of gene expression by means of transcription termination is offered. The model bases on representation about a macrostate of secondary structure in RNA regulatory region between a ribosome and a RNA polymerase, on the formulas of a resonant type defining the value of deceleration of a RNA polymerase by a set of hairpins in the same region. The special attention is given to selection of parameters of model. To check of model the computer simulation is carried out and the dependences of transcription termination probability from the value of concentration charged tRNA are obtained, in particular, and from concentration of amino acid for many regulatory regions in genomes of bacteria (here data are presented for trpE genes in Streptomyces spp., Bradyrhizobium japonicum and Escherichia coli) and at various values of three parameters, which authors consider as the main. The obtained dependences are compounded with the accessible experimental data; including, under the form of the graphs concerning to activity of an enzyme depending on concentration of amino acid (for example, anthranilate synthase from tryptophan in S. venezuela). One possible usage: now attenuation is predicted usually by means of multiple alignment, it needs some sequences; the obtaining with the help of model on an individual sequence characteristic for attenuation or its absence of a curve at approaching parameters could be considered as argument for the benefit of presence or absence of attenuation.