Synthesis Of Catabolic Enzymes Research Articles

Pathogenetic Mechanisms of the Relationship Between Osteoarthritis and Intestinal Dysbiosis

The potential association between dysbiosis of the gut microbiota and osteoarthritis is confirming by a growing number of studies. Given the social significance, the high prevalence of osteoarthritis, and evidences that quantitative and qualitative modification of the gut microbiota affects its progression, it seems important to clarify the underlying mechanisms of this association. Osteoarthritis is a multifactorial joint disease, which is based primarily on the progressive degeneration of articular cartilage. Impaired metabolic activity of chondrocytes, consisting in an imbalance in the extracellular matrix synthesis and degradation processes, causes the persistent release of molecular patterns associated with damage. This leads to the activation of a wide range of innate immune cells receptors and is the basis for the development of an inflammatory reaction in the joint. The involvement of macrophages in the synovial membrane and their activation leads to the production of pro-inflammatory cytokines, leading to the development of chronic low-grade inflammation in the joint, supporting the synthesis of catabolic enzymes by chondrocytes and escalating the cartilage degeneration. Microbial dysbiosis, defined as an adverse modification in the diversity, structure, or metabolic activity of the gut microbiota, is a hidden risk factor, accompanied by metabolic endotoxemia and, consequently, by increased production of pro-inflammatory cytokines, that support the systematic low-grade inflammation and pathophysiological mechanisms of osteoarthritis. It has been shown that dysbiosis of the gut microbiota intestinal takes part in the formation of other osteoarthritis risk factors for, for example, obesity and metabolic disorders. The identification of important interrelated pathophysiological mechanisms of these pathologies will contribute to the development of new pathogenetic treatment methods with their subsequent active introduction into clinical practice.

Genome-wide analysis of the role of GlnR in Streptomyces venezuelae provides new insights into global nitrogen regulation in actinomycetes

BackgroundGlnR is an atypical response regulator found in actinomycetes that modulates the transcription of genes in response to changes in nitrogen availability. We applied a global in vivo approach to identify the GlnR regulon of Streptomyces venezuelae, which, unlike many actinomycetes, grows in a diffuse manner that is suitable for physiological studies. Conditions were defined that facilitated analysis of GlnR-dependent induction of gene expression in response to rapid nitrogen starvation. Microarray analysis identified global transcriptional differences between glnR+ and glnR mutant strains under varying nitrogen conditions. To differentiate between direct and indirect regulatory effects of GlnR, chromatin immuno-precipitation (ChIP) using antibodies specific to a FLAG-tagged GlnR protein, coupled with microarray analysis (ChIP-chip), was used to identify GlnR binding sites throughout the S. venezuelae genome.ResultsGlnR bound to its target sites in both transcriptionally active and apparently inactive forms. Thirty-six GlnR binding sites were identified by ChIP-chip analysis allowing derivation of a consensus GlnR-binding site for S. venezuelae. GlnR-binding regions were associated with genes involved in primary nitrogen metabolism, secondary metabolism, the synthesis of catabolic enzymes and a number of transport-related functions.ConclusionsThe GlnR regulon of S. venezuelae is extensive and impacts on many facets of the organism's biology. GlnR can apparently bind to its target sites in both transcriptionally active and inactive forms.

Proteomic analysis of a non-virulent mutant of the phytopathogenic bacterium Erwinia chrysanthemi deficient in osmoregulated periplasmic glucans: change in protein expression is not restricted to the envelope, but affects general metabolism

Osmoregulated periplasmic glucans (OPGs) are general constituents of the envelope of Gram-negative bacteria. They are required for full virulence of bacterial phytopathogens such as Pseudomonas syringae, Xanthomonas campestris and Erwinia chrysanthemi. E. chrysanthemi is a pectinolytic gamma-proteobacterium that causes soft rot disease on a wide range of plant species. In addition to the loss of virulence, opg mutants exhibit a pleiotropic phenotype that affects motility, bile-salt resistance, exoenzyme secretion, exopolysaccharide synthesis and membrane lipid composition. This is believed to be the first proteomic analysis of an OPG-defective mutant of E. chrysanthemi and it revealed that, in addition to the effects described, catabolic enzyme synthesis was enhanced and there was a greater abundance of some proteins catalysing the folding and degradation of proteins needed for various stress responses. Thus, in the opg mutant strain, loss of virulence was the result of a combination of envelope structure changes and cellular metabolism modifications.

Testosterone-regulated expression of enzymes involved in steroid and aromatic hydrocarbon catabolism in Comamonas testosteroni.

The effect of testosterone as the sole carbon source on protein expression was analyzed in Comamonas testosteroni. Testosterone simultaneously induced the expression of steroid- and aromatic hydrocarbon-catabolizing enzymes and repressed one amino acid-degrading enzyme. It is suggested that steroids play a regulative role in catabolic enzyme synthesis during adaptive growth of C. testosteroni.

Regulatory genes in aspergillus nidulans

A major area for the study of gene regulation in lower eukaryotes has been the coordinated control of catabolic enzyme synthesis. Studies of catabolic gene regulation aim to define how interactions between input signals and regulatory proteins are transmitted to the transcription machinery to bring about changes in gene expression. In the past, mutants altered in the utilization of a wide variety of substrates have been characterized in Aspergillus nidulans. Recently, the development of a transformation system for A. nidulans has meant that molecular techniques can now be combined with the traditional genetic approach.

Methanol metabolism in yeasts: Regulation of the synthesis of catabolic enzymes

The regulation of the synthesis of four dissimilatory enzymes involved in methanol metabolism, namely alcohol oxidase, formaldehyde dehydrogenase, formate dehydrogenase and catalase was investigated in the yeasts Hansenula polymorpha and Kloeckera sp. 2201. Enzyme profiles in cell-free extracts of the two organisms grown under glucose limitation at various dilution rates, suggested that the synthesis of these enzymes is controlled by derepression — represion rather than by induction — repression. Except for alcohol oxidase, the extent to which catabolite repression of the catabolic enzymes was relieved at low dilution rates was similar in both organisms. In Hansenula polymorpha the level of alcohol oxidase in the cells gradually increased with decreasing dilution rate, whilst in Kloeckera sp. 2201 derepression of alcohol oxidase synthesis was only observed at dilution rates below 0.10 h−1 and occurred to a much smaller extent than in Hansenula polymorpha.

Specific induction of catabolism and its relation to repression of biosynthesis in arginine metabolism of Saccharomyces cerevisiae

Experimental results are presented in support of the model previously proposed for specific induction of the synthesis of enzymes for arginine catabolism in Saccharomyces cerevisiae ( Wiame, 1971 a,b ), and its connection with end-product repression of arginine biosynthetic enzymes. The data support the occurrence of negative regulation of metabolism in a eukaryote. Operator regions, one for arginase and another for ornithine transaminase, are identified. The operator mutations are fully constitutive. A mutation compatible with the occurrence of a catabolic represser, CARGR, leads to partial pleiotropic constitutivity. The connection between the induction process and the repression of biosynthetic enzymes is due to a common receptor of metabolic signals, an ambivalent repressor ARGR endowed with the property of a usual repressor for anabolic enzymes and playing the role of inducer at the level of CARGR; this cascade process simulates a positive control. argR − mutations, by producing defective ARGR, “turn on” anabolic enzyme synthesis and “turn off” the synthesis of catabolic enzymes (Fig. 2). The dual role of ARGR is confirmed by the isolation of a mutation argRII d which, in contrast to the defective properties caused by usual argR − mutations, causes a dominant hyperactivity toward induction of a catabolic enzyme, but retains recessive hypoactivity toward repression of an anabolic enzyme. Such an ambivalent repressor is a function necessary for mutual, balanced exclusion between opposite metabolisms. Many operator constitutive mutations for arginase, cargA + O −, change the level of enzyme to a similar value, thus defining a genetic function. One of these mutations, cargA + O h, in addition to having unusual genetic behaviour, leads to production of twice as much arginase as cargA + O −. This suggests the existence of another genetic region near the structural gene for this enzyme and an additional regulatory function to be analyzed in a separate paper ( Dubois & Wiame, 1978).

Permease-specific mutations in Salmonella typhimurium and Escherichia coli that release the glycerol, maltose, melibiose, and lactose transport systems from regulation by the phosphoenolpyruvate:sugar phosphotransferase system

Several carbohydrate permease systems in Salmonella typhimurium and Escherichia coli are sensitive to regulation by the phosphoenolpyruvate:sugar phosphotransferase system. Mutant Salmonella strains were isolated in which individual transport systems had been rendered insensitive to regulation by sugar substrates of the phosphotransferase system. In one such strain, glycerol uptake was insensitive to regulation; in another, the maltose transport system was resistant to inhibition; and in a third, the regulatory mutation specifically rendered the melibiose permease insensitive to regulation. An analogous mutation in E. coli abolished inhibition of the transport of beta-galactosides via the lactose permease system. The mutations were mapped near the genes which code for the affected transport proteins. The regulatory mutations rendered utilization of the particular carbohydrates resistant to inhibition and synthesis of the corresponding catabolic enzymes partially insensitive to repressive control by sugar substrates of the phosphotransferase system. Studies of repression of beta-galactosidase synthesis in E. coli were conducted with both lactose and isopropyl beta-thiogalactoside as exogenous sources of inducer. Employing high concentrations of isopropyl beta-thiogalactoside, repression of beta-galactosidase synthesis was not altered by the lactose-specific transport regulation-resistant mutation. By contrast, the more severe repression observed with lactose as the exogenous source of inducer was partially abolished by this regulatory mutation. The results support the conclusions that several transport systems, including the lactose permease system, are subject to allosteric regulation and that inhibition of inducer uptake is a primary cause of the repression of catabolic enzyme synthesis.

The mechanism of sugar‐dependent repression of synthesis of catabolic enzymes in escherichia coli

Previous studies have indicated that the Escherichia coli adenylate cyclase (AC) activity is controlled by an interaction with the phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS). A model for the regulation of AC involving the phosphorylation state of the PTS is described. Kinectic studies support the concept that the velocity of AC is determined by the opposing contributions of PEP-dependent phosphorylation (V1) and sugar-dependent dephosphorylation (V2) of the PTS proteins according to the expression percent VAC=100/[1 + (Max V2/Max V1)]. Physiological parameters influencing the rate of the PTS are discussed in the framework of their effects on cAMP metabolism. Factors that increase cellular concentration of PEP (and stimulate V1) appear to enhance AC activity while increases in extracellular sugar concentration (which stimulate V2) or internal levels of pyruvate (which inhibit V1) inhibit the activity of this enzyme.

Effects of crp mutations on adenosine 3',5'-monophosphate metabolism in Salmonella typhimurium

Wild-type Salmonella typhimurium could not grow with exogenous cyclic adenosine 3',5'-monophosphate (AMP) as the sole source of phosphate, but mutants capable of cyclic AMP utilization could be isolated provided the parental strain contained a functional cyclic AMP phosphodiesterase.All cyclic AMP-utilizing mutants had the growth and fermentation properties of cyclic AMP receptor protein (crp) mutants, and some lacked cyclic AMP binding activity in vitro. The genetic defect in each such mutant was due to a single point mutation, which was co-transducible with cysG. crp mutants isolated by alternative procedures also exhibited the capacity to utilize cyclic AMP. crp mutants synthesized cyclic AMP at increased rates and contained enhanced cellular cyclic AMP levels relative to the parental strains, regardless of whether or not cyclic AMP phosphodiesterase was active. Moreover, adenylate cyclase activity in vivo was less sensitive to regulation by glucose, possibly because the enzyme II complexes of the phosphotransferase system, responsible for glucose transport and phosphorylation, could not be induced to maximal levels. This possibility was strengthened by the observation that enzyme II activity (measured both in vitro by sugar phosphorylation and in vivo by sugar transport and chemotaxis) was inducible in the parental strain but not in crp mutants. The results suggest that the cyclic AMP receptor protein regulates cyclic AMP metabolism as well as catabolic enzyme synthesis.

Transient repression of catabolite-sensitive enzyme synthesis elicited by 2,4-dinitrophenol

Transient inhibition of catabolic enzyme synthesis in Escherichia coli occurred when a low concentration of 2,4-dinitrophenol (DNP) was simultaneously added with inducer. Using mutant strains defective for gamma-gene product or constitutive for lac enzymes, it was found that the inhibition is not due to the exclusion of inducer by uncoupling. The addition of cyclic adenosine 3',5'-monophosphate overcame repression. The components of the lac operon coordinately responded to DNP inhibition. From deoxyribonucleic acid-ribonucleic acid hybridization experiments, it was found that the inhibition of beta-galactosidase induction occurred at the level of messenger ribonucleic acid synthesis specific for the lac operon. It seems probable that DNP represses induction in a similar manner to that of transient repression observed upon the addition of glucose. Furthermore, it was found that transient repression disappeared if cells were preincubated with DNP before induction. This indicates that new contact of cells with DNP is obligatory for transient repression. From these results, it is suggested that the cell membrane may be responsible for regulation of catabolite-sensitive enzyme synthesis.

Effects of 32P decay on enzyme synthesis

Cultures of Escherichia coli 15T − inactivated by 32 P decay to a survival of 0·1% are capable of synthesizing phosphatase at about 25% of the rate found in completely viable cells. These cultures also retain a similar fraction of their ability to form β -galactosidase, if no energy source is present during the induction. If glycerol is added to the medium, however, no β -galactosidase is formed. The earlier observation of an apparent concomitant decline in enzyme-forming capacity and viability following 32 P decay can therefore be attributed to repression on the synthesis of catabolic enzymes in cells in which the rate of catabolism exceeds the rate of growth.