Systemic and regional hemodynamic reactions to metabolic stress caused by 2-deoxyglucose

Changes in parameters of systemic and regional hemodynamic, elicited by intraarterial administration of 250 or 500 mg/kg of 2-deoxy-D-glucose (2-DG) were studied in the awake Wistar rats with microsphere technique. Measurements were performed before, 15-and 40-min after 2-DG administration. Significant decrease in the heart rate as well as increase in stroke volume were observed 15 min after 2-DG. It was a tendency to increase in cardiac output. Blood flow in skin and skeletal muscles were decreased whereas in the brain, heart, adrenal glands and small intestine there were significant increases in the blood flow. We conclude that hemodynamic responses to 2-DG reflect the effects of humoral (adrenaline) and central sympathetic factors.     

Optimizing metabolic pathways by screening for feasible synthetic reactions

Background

Reconstruction of genome-scale metabolic networks has resulted in models capable of reproducing experimentally observed biomass yield/growth rates and predicting the effect of alterations in metabolism for biotechnological applications. The existing studies rely on modifying the metabolic network of an investigated organism by removing or inserting reactions taken either from evolutionary similar organisms or from databases of biochemical reactions (e.g., KEGG). A potential disadvantage of these knowledge-driven approaches is that the result is biased towards known reactions, as such approaches do not account for the possibility of including novel enzymes, together with the reactions they catalyze.

Results

Here, we explore the alternative of increasing biomass yield in three model organisms, namely Bacillus subtilis, Escherichia coli, and Hordeum vulgare, by applying small, chemically feasible network modifications. We use the predicted and experimentally confirmed growth rates of the wild-type networks as reference values and determine the effect of inserting mass-balanced, thermodynamically feasible reactions on predictions of growth rate by using flux balance analysis.

Conclusions

While many replacements of existing reactions naturally lead to a decrease or complete loss of biomass production ability, in all three investigated organisms we find feasible modifications which facilitate a significant increase in this biological function. We focus on modifications with feasible chemical properties and a significant increase in biomass yield. The results demonstrate that small modifications are sufficient to substantially alter biomass yield in the three organisms. The method can be used to predict the effect of targeted modifications on the yield of any set of metabolites (e.g., ethanol), thus providing a computational framework for synthetic metabolic engineering.     

Chromosome imbalances in endometrial adenocarcinomas: a possible adaptation to abnormal metabolic pathways

Chromosome studies of endometrial carcinomas show several recurrent trisomies or tetrasomies: 1 (long arm), 10, 2, 7, 12, 3 and possibly X (long arm). These chromosomes or chromosome segments carry the majority of the genes coding for enzymes of glucidic metabolism, citrate cycle, and initial steps of nucleotide synthesis. Their excess, which does not appear as a primary event in tumorigenesis, is interpreted as an adaptation of the cancer cells to abnormalities of metabolic pathways. The increase of gene copies, by chromosome duplication, would facilitate the synthesis of enzymes the activity of which is increased. If this view is correct and has a general value, it would mean that, in addition to primary chromosome changes, which may induce oncogene activation, most anomalies, which are obviously secondary, may reflect a disturbance of metabolic pathways coded by housekeeping genes.     

Partial randomization of the four sequential amidation reactions catalyzed by cobyric acid synthetase with a single point mutation

Cobyric acid synthetase (CbiP) from Salmonella typhimurium catalyzes the glutamine and ATP-dependent amidation of carboxylates b, d, e, and g within adenosyl cobyrinic acid a,c-diamide. After each round of catalysis the partially amidated intermediates are released into solution and the four carboxylates are amidated in the sequential order of e, d, b, and g for the wild type enzyme. In the presence of [gamma-18O4]-ATP and adenosyl cobyrinic a,c-diamide the enzyme will catalyze the positional isotope exchange of the betagamma-bridge oxygen with the two beta-nonbridge oxygens. These results support the proposal that ATP is used to activate the carboxylate groups via the formation of a phosphorylated intermediate. CbiP catalyzes the hydrolysis of glutamine in the absence of ATP or adenosyl cobyrinic acid a,c-diamide, but the rate of glutamine hydrolysis is enhanced by a factor of 60 in the presence of these two substrates together. This result suggests that the formation of the phosphorylated intermediate is coupled to the activation of the site utilized for the hydrolysis of glutamine. However, the rate of glutamine hydrolysis is approximately 2.5 times the rate of ADP formation, indicating that the two active sites are partially uncoupled from one another and that some of the ammonia from glutamine hydrolysis leaks into the bulk solution. The mutation of D146 to either alanine or asparagine results in a protein that is able to catalyze the formation of cobyric acid. However, the strict amidation order observed with the wild type CbiP is partially randomized with carboxylate b being amidated last. With the D146N mutant, the predominant pathway occurs in the sequence d, e, g, and b. It is proposed that this residue enforces the amidation order in the wild type enzyme via charge-charge repulsion between the side chain carboxylate and the carboxylates of the substrate.     

Phenomenological definition of response times with application to metabolic reactions

The metabolic response time, i.e. the delay the system introduces in the response to an input flux, is considered. A novel phenomenological definition is presented, which is valid for any kind of behavior, including transitory or permanent oscillatory responses. In order to calculate the response time of single-input systems, output fluxes have to be deconvoluted with the input flux. The bases for this are established. The resulting function (unit impulse response in time-invariant linear systems) is transformed by subtracting its final state, taking the absolute value and normalizing by the resulting area, so that a norm can be applied that weights the response at every time. This response time can also be interpreted as an average. It coincides with the transition (characteristic) time of an output flux, provided that the input is performed instantaneously (step function). A strictly non-negative response function is needed for the response time to be interpreted as a mass balance. A simple example is used to study the deviation otherwise. The method is advantageous in that it provides clues on the phenomenological behavior of biochemical systems. For example, deconvolution reveals the intrinsic oscillation-generating mechanism of an allosteric enzyme, which becomes hidden when the input flux increases in a slow way. This is illustrated by means of a model.     

Rates of membrane-associated reactions: reduction of dimensionality revisited

The hypothesis that reactions associated with intracellular membranes enjoy a kinetic advantage from a reduced dimensionality for diffusion is inconsistent with available data on lateral diffusion rates, membrane-substrate affinities, and endogenous concentrations of enzymes and their aqueous substrates.     

Saprotrophic bacteria as a possible means of controlling the immune status of the body through regulation of metabolic reactions

An analysis of the literature allowed a theoretical grounding of the possibility of microbial control of the immune status of the organism by the use of saprotrophic bacteria regulating its metabolic status (i.e., its enzymatic reactions). The main objective of the microbial control is protection from infections caused by conditionally pathogenic microflora. Bacterial formulations can produce the following effects: (1) a decrease in the activities of the oxidation system, glucuronyl transferase, and NAD⁺ glycohydrolase and an increase in the activity of glucose-6-phosphate dehydrogenase in hepatic microsomes; (2) an increase or a decrease in acetylation activity in the liver and its increase in lymphocytes; (3) an increase in the activities of the enzymes of glycolysis, the hexose monophosphate shunt, and the NADPH oxidase system, as well as succinate and glutamate dehydrogenases, acid phosphatase, -naphthyl acetate esterase, and nonspecific esterase, in immunocompetent cells; and/or (4) stimulation of humoral and cell-mediated immunity. To achieve microbial control over the immune status of the human organism, it is necessary (1) to study the correlations between the pharmacokinetics of test substances, the activities of enzymes involved in their metabolism, and humoral and cell mediated immune reactions; (2) to determine the metabolic phenotypes of individuals; (3) to identify and systematize the normal saprotrophic microflora of each individual; (4) to elucidate the molecular mechanisms of biochemical effects exerted by saprotrophic bacteria; and (5) to select specific strains of saprotrophic bacteria that secrete substances regulating the activities of the above enzymes and metabolic processes. Different tactics of the microbial control of the individual immunity should be selected for subjects with different phenotypes.Translated from Fiziologiya Cheloveka, Vol. 31, No. 1, 2005, pp. 88–99.Original Russian Text Copyright © 2005 by Piruzyan, Mikhailovskii.This work is based on an original concept suggested by L.A. Piruzyan.     

Effect of hematocrit reduction on hormonal and metabolic responses to exercise

We wished to determine the effect of a 25% hematocrit reduction on glucoregulatory hormone release and glucose fluxes during exercise. In five anemic dogs, plasma glucose fell by 21 mg/dl and in five controls by 7 mg/dl by the end of the 90-min exercise period. After 50 min of exercise, hepatic glucose production (Ra) and glucose metabolic clearance rate (MCR) began to rise disproportionately in anemics compared with controls. By the end of exercise, the increase in Ra was almost threefold higher (delta 15.1 +/- 3.4 vs. delta 5.2 +/- 1.3 mg X kg-1 X min-1) and MCR nearly fourfold (delta 24.6 +/- 8.8 vs. delta 6.5 +/- 1.3 ml X kg-1 X min-1). Exercise with anemia, in relation to controls resulted in elevated levels of glucagon [immunoreactive glucagon (IRG) delta 1,283 +/- 507 vs delta 514 +/- 99 pg/ml], norepinephrine (delta 1,592 +/- 280 vs. delta 590 +/- 155 pg/ml), epinephrine (delta 2,293 +/- 994 vs. delta 385 +/- 186 pg/ml), cortisol (delta 6.7 +/- 2.2 vs. delta 2.1 +/- 1.0 micrograms/dl) and lactate (delta 12.1 +/- 2.2 vs. delta 4.2 +/- 1.8 mg/dl) after 90 min. Immunoreactive insulin and free fatty acids were similar in both groups. In conclusion, exercise with a 25% hematocrit reduction results in 1) elevated lactate, norepinephrine, epinephrine, cortisol, and IRG levels, 2) an increased Ra which is likely related to the increased counterregulatory response, and 3) we speculate that a near fourfold increase in MCR is related to metabolic changes due to hypoxia in working muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The possible metabolic diversions adapted by the cockroach, Periplaneta americana to counteract the toxicity of fenvalerate

Effects of sublethal doses of fenvalerate through topical application were monitored in the central nervous system (CNS) of P. americana. A decrease in total and soluble proteins with an increase in free amino acids, alanine aminotransferase (AlAT) and aspartate aminotransferase (AAT) was observed during fenvalerate toxicity. Further the levels of glycogen, pyruvate and activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) dropped significantly. Lactate content and lactate dehydrogenase (LDH) activity also showed an elevation following fenvalerate toxicity.