Induction Of Enzyme Synthesis Research Articles

A neo-logistic model for the growth of bacteria

We propose a neo-logistic model that can describe bacterial growth data precisely. This model is not derived by modifying the logistic model formally, but by incorporating the synthesis of inducible enzymes into the logistic model indirectly. Therefore, the meaning of the parameters of the neo-logistic model becomes physically clear. The neo-logistic model can approximate bacterial growth much more accurately than previous models, and can accurately predict the order of the saturated number of bacteria in the stationary phase from the initial growth data.

Consistency of cybernetic variables with gene expression profiles: A more rigorous test.

Diauxic growth of Escherichia coli is driven by a host of internal, complex regulatory actions. In this classic scenario of cellular control, the cell employs a rational algorithm to modulate its metabolism in a competitive fashion. Cybernetic models of metabolism, whose development now spans three decades, were first formulated to describe regulation of cells in complex, multi-substrate environments. They modeled this scenario using the hypothesis that the formation of the enzymatic machinery is regulated to maximize a return on investment. While this assumption is made on the basis of logical arguments rooted in evolutionary principles, little effort has been taken to validate if enzymes are truly synthesized in the same fashion that is predicted by cybernetic variables. This work revisits the original cybernetic models describing diauxic growth and compares their predictions of enzyme synthesis control with time series gene expression data in microarray and qRT-PCR formats. Three separate studies are made for two different strains of E. coli. The first is for the growth of E. coli BW25113 on a mixture of glucose and acetate, whose gene expression changes are metered by microarray. Another is also for the sequential consumption of glucose and acetate but involves strain MG1655 and employs qRT-PCR. The final is for E. coli MG1655 on glucose and lactose. By demonstrating how cybernetic variables for induced enzyme synthesis mimic the behavior of transcriptional data, a strong argument for using cybernetic models is made. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:858-867, 2018.

In vitro Studies of the Antibody Response: Antibodies of Different Specificity are Made in Different Populations of Cells.

In vitro Studies of the Antibody Response: Antibodies of Different Specificity are Made in Different Populations of Cells.

Effect of Various Physiological Parameters and Different Carbon Sources on Cellulase and Xylanase Induction by Different Strains of Trichoderma Species

The recent interest in bioconversion of cellulosic wastes to value added chemicals has led to extensive studies on microorganisms capable of producing the enzyme. Cellulases are multi-enzyme complex proteins that catalyze the conversion of cellulose to glucose. Trichoderma is the main industrial source of cellulases and hemicellulases used to depolymerize plant biomass to simple sugars that are converted to chemical intermediates such as biofuels. The current study was carried out to isolate and characterize different Trichoderma species for successful applications. The strains were characterized for cellulase and xylanase assays to determine their extracellular hydrolytic activities. Expression of xylanase was induced maximally by xylan and repressed by glucose. Moreover, a comparative analysis was done between two different Trichoderma species which revealed that Trichoderma harzianum and Trichoderma harzianum Th-azad shows better enzyme activity than T. viride 01PP. Furthermore, optimal conditions for enzyme activity and induction of enzyme synthesis were also determined. The results revealed that the optimal pH, temperature and incubation time for cellulase production was found to be 5.5, 28° C and 120 h respectively. In the present study, we also evaluate the effects of wheat bran, cellulose powder as carbon sources for cellulase and xylanase production. The result showed that the enzyme production was highest with wheat bran as sole source ofcarbon.

Improvement of polygalacturonase production at high temperature by mixed culture of Aspergillus niger and Saccharomyces cerevisiae

Catabolic repression in the synthesis of inducible enzymes by glucose, fructose, and intermediates of the glycolytic cycle has been observed in many microorganisms. In order to enhance the polygalacturonase (PG) production of Aspergillus niger GJ-2, Saccharomyces cerevisiae J-1 was inoculated to the medium at 12h of culture, which resulted in a significant improvement of PG production. It was also found that maximum PG activity of 512.7U/ml was obtained at 37°C in the mixed culture, which was nearly twofold higher than that of the culture without the inoculation of S. cerevisiae J-1.

5553 POSTER Second radical irradiation in head and neck cancer patients – retrospective study

The increase in DT diaphorase activity after treatment of rats with 3-Meyhylcholantrene (MC) seems to be due to an induced enzyme synthesis. Not only liver but also other tissues show an increased DT diaphorase activity after MC-treatment. This increase parallels that of the aryl hydrocarbon monooxygenase (AHM) activity except in heart, where only DT diaphorase activity increases. This indicates a difference in gene expression between the inductions of DT diaphorase and the AHM system. Microsomal hydroxylation of benzo(a)pyrene (BP) leads to an inhibition of DT diaphorase with a simultanous decrease in dicoumarol sensitivity of the enzyme. Probably a product of BP metabolism is responsible for these effects.

Induction of HSPs and antioxidant defense enzymes during activation of free radical oxidation at the early stage of hypokinesia

We studied the stress component of the early stage of hypokinesia during hindlimb unloading. The intensity of free radical processes was evaluated and the content of protective proteins (antioxidant defense enzymes and proteins of the HSP family) was measured in the heart and liver. Three-hour hypokinesia increased the content of constitutive protective proteins, including hemoxygenase-2 and antioxidant defense enzymes, in the heart. Hypokinesia for 72 h was accompanied by more potent activation of antioxidant defense enzymes and increase in the content of inducible hemoxygenase-1, which leads to partial compensation of activated free radical oxidation. In the liver, hypokinesia of different duration suppressed the protective systems: the synthesis of inducible and constitutive hemoxygenases and antioxidant defense enzymes decreased, while the sensitivity of liver membrane structures to reactive oxygen species increased. We revealed a tissue-specific response to hypokinesia: pronounced damaging effect predominated in the liver and partial compensation of elevated production of reactive oxygen species was observed in the heart due to activation of protective systems.

Effect of DNA looping on the induction kinetics of the lac operon

The induction of the lac operon follows cooperative kinetics. The first mechanistic model of these kinetics is the de facto standard in the modeling literature [Yagil, G., Yagil, E., 1971. On the relation between effector concentration and the rate of induced enzyme synthesis. Biophys. J. 11, 11–17]. Yet, subsequent studies have shown that the model is based on incorrect assumptions. Specifically, the repressor is a tetramer with four (not two) inducer-binding sites, and the operon contains two auxiliary operators (in addition to the main operator). Furthermore, these structural features are crucial for the formation of DNA loops, the key determinants of lac repression and induction. Indeed, the repression is determined almost entirely ( > 95 % ) by the looped complexes [Oehler, S., Eismann, E.R., Krämer, H., Müller-Hill, B., 1990. The three operators of the lac operon cooperate in repression. EMBO J. 9(4), 973–979], and the pronounced cooperativity of the induction curve hinges upon the existence of the looped complexes [Oehler, S., Alberti, S., Müller-Hill, B., 2006. Induction of the lac promoter in the absence of DNA loops and the stoichiometry of induction. Nucleic Acids Res. 34(2), 606–612]. Here, we formulate a model of lac induction taking due account of the tetrameric structure of the repressor and the existence of looped complexes. We show that: (1) The kinetics are significantly more cooperative than those predicted by the Yagil and Yagil model. The cooperativity is higher because the formation of looped complexes is easily abolished by repressor–inducer binding. (2) The model provides good fits to the repression data for cells containing wild-type tetrameric or mutant dimeric repressor, as well as the induction curves for 6 different strains of Escherichia coli. It also implies that the ratios of certain looped and non-looped complexes are independent of inducer and repressor levels, a conclusion that can be rigorously tested by gel electrophoresis. (3) Repressor overexpression dramatically increases the cooperativity of the induction curve. This suggests that repressor overexpression can induce bistability in systems, such as growth of E. coli on lactose, that are otherwise monostable.

Nutritional conditions affecting induced enzyme synthesis in Streptomyces violaceus

Nutritional conditions affecting induced enzyme synthesis in Streptomyces violaceus

Heat stress preconditioning and delayed myocardial protection: what is new?

As other preconditioning phenomena, heat stress is able to induce a delayed myocardial protection against ischaemia-reperfusion injury by preserving ventricular function, preventing arrhythmia occurrence and reducing cellular necrosis. The development of heat stress response has been extensively studied in order to characterize the different steps of this form of preconditioning. It appears that chemical signals (such as nitric oxide, reactive oxygen species (ROS)) released by sublethal hyperthermic stress trigger a complex cascade of signalling events that include activation of protein kinase C (PKC) and mitogen-activated protein kinases (MAPK) and culminate in increased synthesis of inducible nitric oxide synthase, cyclooxygenase-2, antioxidant enzymes and protective proteins such as heat stress proteins (Hsps). A better understanding of this powerful protective adaptation of the cardiomyocyte is essential for the development of clinical applications and the design of cardioprotective pharmacological agents. The purpose of this letter is to review current information regarding the characteristics of heat stress preconditioning compared to other forms of late preconditioning.

Properties of mutants of bacteria belonging to the genus Erwinia devoid of common components of the phosphoenolpyruvate-dependent phosphotransferase system

Biochemical consequences of mutational damage to common components of the Erwinia phosphoenolpyruvate-dependent phosphotransferase system (the HPr protein and enzyme I) were studied. The transport of glucose, mannose, fructose, and mannitol in Erwinia was shown to require a preliminary induction of proteins of the phosphotransferase system. A drastic decrease in the rate of the transport of these carbohydrates was observed in ptsI and ptsH mutants. A disturbance in the common components suppresses the synthesis of inducible enzymes (beta-galactosidase, complexes of pectolyases and cellulases) and renders it resistant to catabolite repression by glucose, but mutants were shown to retain intracellular cAMP content. Erwinia mutants devoid of common components of the system lack phytopathogenic features. The appearance of an intact ptsI allele in the cell completely corrected pleiotropic disturbances in these mutants.

Viable but nonculturable bacteria: a survival strategy.

When bacteria are introduced into a new environment, environmental changes with which they are confronted may include temperature, nutrient concentration, salinity, osmotic pressure, and pH. Bacterial cells dynamically adapt to these shifts in their environment, employing a variety of genetic mechanisms. Bacteria, with the ability to utilize constitutive and inducible enzyme synthesis, can accommodate to growth-limiting nutrients and adjust or reroute metabolic pathways to avoid metabolic and/or structural disruption caused by specific nutrient limitations. Furthermore, they are able to coordinate their rates of synthesis to maintain their cellular structure and function. These adaptive capabilities provide bacterial cells with an extraordinary set of mechanisms by which they are able to respond to their surrounding environment and survive.

Differential Dissolved Organic Nitrogen Availability and Bacterial Aminopeptidase Activity in Limnic and Marine Waters.

Abstract Nitrogen often limits primary production in marine ecosystems and its loading from terrestrial sources is the major cause of enhanced coastal eutrophication worldwide. About 70% of nitrogen transported by rivers globally is dissolved organic nitrogen (DON). Therefore, terrestrial DON is potentially an important component of the N dynamics in aquatic ecosystems, but the bioavailability of this organic nitrogen is poorly known. Bacterial extracellular hydrolysis of polymers is a bottleneck in the utilization of natural dissolved organic matter, mostly consisting of high molecular weight compounds. To study the bacterial utilization and extracellular enzymatic hydrolysis of DON, we developed a bioassay employing natural DON as the only N source, and N as the limiting nutrient. Bacterial cell density and activity of an unspecific aminopeptidase (AMPase) were followed in the cultures. Natural DON stimulated the cell-specific AMPase activity. Furthermore, refractory and humus-rich DOM caused a stronger stimulation than labile DOM. We propose that the previously reported inhibitory effect of humic substances on enzyme activity was outweighed by the induction of enzyme synthesis caused by refractory substrates. AMPase activity and the estimated DON bioavailability were more than twofold higher in seawater than in freshwater with identical substrate additions. This indicates that hydrolysis and turnover of land-derived DON is enhanced when it enters coastal marine waters, enabling it to support elevated bacterioplankton and phytoplankton growth.http://link.springer-ny.com/link/service/journals/00248/bibs/38n3p264.html</hea

Synthesis of extracellular lipase by a strain ofPseudomonas fluorescensisolated from raw camel milk

Ten strains of psychrotrophic bacteria were isolated from raw camel milk and were arranged according to their lipase production. Lipolytic activities ranged between 0.26 to 3.43 meq of palmetic acid 100 g-;1of bovine milk fat h-;1.Pseudomonas fluorescensRM4was the most active strain. This bacterium could grow and secrete lipase over a wide range of temperatures. The optimum temperature for growth was 37°C, and the maximum lipase production was at 25°C. Growth was maximal after 96 h of incubation at 25°C, and lipase activity was maximal at 72 h post-inoculation at 25°C (during the late logarithmic phase). Shaking of the cultures (100 rpm) led to an increase in both growth and enzyme activities. Pseudomonas fluorescensRM4was able to grow and secrete lipase over a pH range of 5.5-;8.50. Synthesis of the enzyme appeared to be inducible because no enzyme was detected in the absence of organic nitrogen. Supplementation of the basal medium with milk proteins enhanced lipase production. Tryptophan and lysine induced enzyme synthesis most effectively. Addition of 4 g l-;1of glucose to broth stimulated both growth and production of lipase. Beyond this level of supplementation, lipase activity was considerably depressed.

Tracheal ligation and mechanical ventilation do not improve the antioxidant enzyme status in the lamb model of congenital diaphragmatic hernia

Background/Purpose: The antioxidant enzyme (AOE) system is the primary intracellular defense system of the lung against oxygen toxicity. The authors recently demonstrated depressed levels of catalase, glutathione peroxidase, and superoxide dismutase in congenital diaphragmatic hernia (CDH) lambs compared with controls. The aim of this study was to determine whether tracheal ligation (TL) or mechanical ventilation (recently shown to stimulate growth and surfactant metabolism, respectively) could induce an elevation in AOE activity. Methods: Four nonventilated lambs with surgically created CDH and TL and five CDH lambs ventilated for 4 hours were studied. Lung tissue was analyzed for AOE and the results compared with untreated CDH lambs. Results: Both ventilation and TL failed to elevate AOE activity above that of untreated CDH lambs. Conclusions: The dataprovide further evidence that TL does not improve lung metabolism or maturation. Mechanical ventilation, which often involves high oxygen delivery, is a necessary and often beneficial therapeutic modality. In the CDH neonate compromised not only by low baseline levels of the AOE, but also by an inability to induce enzyme synthesis in response to hyperoxia, mechanical ventilation may, by causing lung injury, be contributing to the high morbidity and mortality rate associated with CDH.

Physiological control on the expression and secretion of Candida rugosa lipase

The fungus Candida rugosa secretes an extracellular lipase whose production is induced by the addition of fatty acids to the culture broth. This lipase is indeed composed by several protein isoforms partly differing in their catalytic properties. Synthesis and secretion of lipase proteins by C. rugosa cells were studied in culture media containing either glucose or oleic acid as the carbon source. It was shown that, according to their regulation, lipase-encoding genes might be grouped in two classes, one of which is constitutively expressed and the other is induced by fatty acids. The synthesis of inducible enzymes is inhibited at the level of transcription by the addition of glucose and, conversely, oleic acid appears to hinder the synthesis of the constitutive lipase. Growth conditions supporting high level expression both in batch and in continuous culture give rise to the intracellular accumulation of enzyme, possibly due to the existence of a rate-limiting step in the transport of the newly synthesized protein. These results suggest the possibility to develop fermentation processes aimed at the control of the enzyme composition.

Regulation by Galacturonic Acid of Pectinolytic Enzyme Production by Sclerotinia sclerotiorum

Production of polygalacturonases and pectinases from Sclerotinia sclerotiorum was induced in vitro by galacturonic acid. The inductive effect of galacturonic acid was abolished by the presence of glucose, leading to a basal enzyme production. Zymograms of extracellular enzymes showed that galacturonic acid induced the synthesis of six polygalacturonase and one pectin-methylesterase isoforms. Immunoblotting revealed that an exo-polygalacturonase and an exo-polymethylgalacturonase were secreted in all conditions. They are not glucose repressed and not regulated by galacturonic acid. These constitutive enzymes provide the pathogen with the inherent ability to release galacturonic acid from plant cell walls and to trigger inducible enzyme synthesis.

Regulation of pectin methylesterase and polygalacturonate lyase activity during differentiation of infection structures in Uromyces viciae-fabae

the kinetics of their synthesis and the Kms of the three major isoenzymes were determined. The enzyme activity was formed independently of the presence of its substrate and its regulation was thus differentiation-specific. A single PL was induced when haustoriaI mother cells were formed and its synthesis appeared to be controlled by both the developmental stage of infection structures and the availability of its substrate. Polygalacturonate concentrations lower than 0'025 mg ml- 1 induced enzyme synthesis, and at 0'25 mg ml- 1 the induction proces's appeared to be saturated. Enzyme formation in the presence of 50 mM glucose, fructose or sucrose suggested that neither pectic enzyme was subject to catabolite repression. Significant proportions of PME (approx. 57%) and PL (approx. 76%) activity were located extracellularly in 24-h-old differentiated infection structures and could contribute to the establishment of the parasite. Physico-chemical and kinetic properties of the enzymes and associated alterations of the apoplastic pH of infected host plants appeared to be important factors in the success of infection and could explain the restriction of cell wall damage at the penetration site usually observed in interactions involving obligately biotrophic fungi.

Nitrofurantoin: mechanism of action and implications for resistance development in common uropathogens.

Nitrofurantoin is an effective urinary tract antibacterial to which no clinically significant resistance development has occurred. We have previously shown that nitrofurantoin susceptibility in bacteria correlates with the presence of bacterial nitroreductases which convert nitrofurantoin to highly reactive electrophilic intermediates. These intermediates were shown to attack bacterial ribosomal proteins non-specifically, causing complete inhibition of protein synthesis. In the present study, we confirm previous reports that low concentrations of nitrofurantoin specifically inhibit inducible enzyme synthesis in bacteria, and show that this inhibition occurs at levels equivalent to the MICs of nitrofurantoin for several bacterial species. Our previous studies had shown that nitrofurantoin at different concentrations interacts with bacterial ribosomal proteins in qualitatively the same fashion; we now report that quantitative differences are seen in the labelling observed at different nitrofurantoin concentrations and discuss these differences as they may relate to the inhibition of inducible enzyme synthesis. In addition, we have now demonstrated the existence of a novel mechanism of action for nitrofurantoin which does not require the production of reactive nitrofurantoin metabolites by bacterial reductases. The lack of clinically significant bacterial resistance development to nitrofurantoin is likely due to the combination of nitrofurantoin's multiple sites of attack and multiple mechanisms of action.

Estimation of the intracellular free ADP concentration by 19F NMR studies of fluorine-labeled yeast phosphoglycerate kinase in vivo.

Yeast phosphoglycerate kinase was selectively fluorine-labeled in vivo by inducing enzyme synthesis in stationary phase cells in the presence of 5-fluorotryptophan. Inducible expression was obtained using a galactose-inducible expression vector containing the yeast phosphoglycerate kinase coding sequence. 19F NMR measurements on intact cells showed two resolved resonances, from the two tryptophan residues in the protein, which underwent reversible changes in chemical shift under different metabolic conditions. Measurements in vitro showed that the difference in the chemical shifts of these two resonances was dependent on the adenine nucleotide concentration, in particular the MgADP concentration. A comparison of the spectra obtained in vitro with those obtained from the intact cell indicated that in glucose-fed cells the cytosolic free MgADP concentration was less than 50 microM, which is significantly lower than the concentrations measured in whole-cell extracts.