scholarly journals Control analysis of transition times in metabolic systems

1990 ◽  
Vol 265 (1) ◽  
pp. 195-202 ◽  
Author(s):  
E Meléndez-Hevia ◽  
N V Torres ◽  
J Sicilia ◽  
H Kacser
Keyword(s):  
Steady State ◽  
Temporal Characteristic ◽  
Negative Control ◽  
Control Analysis ◽  
Metabolic System ◽  
Steady State Flux ◽  
Metabolic Systems ◽  
Summation Theorem ◽  
Transition Times ◽  
Control Coefficients

The transition time, tau, of a metabolic system is defined as the ratio of the metabolite concentrations in the system, sigma, to the steady-state flux, J. Its value reflects a temporal characteristic of the system as it relaxes towards the steady state. Like other systemic properties, the value of tau will be a function of the enzyme activities in the system. The influence of a particular enzyme activity on tau can be quantified by a Control Coefficient, C tau ei. We show that it is possible to derive a Summation Theorem sigma ni = 1 C tau ei = -1 and a Connectivity Theorem sigma ni = 1 C tau ei.epsilon viSk = -Sk/sigma. We establish a ‘sign rule’ that predicts the order of positive and negative Control Coefficients in a sequence.

scholarly journals Integration of temporal analysis and control analysis of metabolic systems

1990 ◽  
Vol 269 (1) ◽  
pp. 255-259 ◽  
Author(s):  
J S Easterby
Keyword(s):  
Steady State ◽  
Transient Response ◽  
Temporal Analysis ◽  
Metabolic Control Analysis ◽  
Control Analysis ◽  
Control Coefficient ◽  
Temporal Control ◽  
Transient Time ◽  
Metabolic Systems ◽  
Control Coefficients

A theory is developed that integrates approaches to the analysis of pathway transient response and metabolic control analysis. A Temporal Control Coefficient is defined that is a measure of the system's transient response to modulation of enzyme activity or concentration. The approach allows for the analysis of the establishment of a steady state from rest, of the system's ‘agility’ of response to minor perturbations of a pre-existing steady state and of the macroscopic transition between steady states. In the last-mentioned case it is shown that, like the transient time itself, the control of transient response retains the property of independence from the mechanism of the transition. In consequence, the Temporal Control Coefficient can be defined in terms of the control properties of the initial and final states alone without reference to the mechanism of transition. A summation property is shown to apply to the Temporal Control Coefficients in each case. Connectivity relationships between elasticities and Temporal Control Coefficients are also established.

Regulation analysis of energy metabolism.

1997 ◽  
Vol 200 (2) ◽  
pp. 193-202 ◽  
Author(s):  
M D Brand
Keyword(s):  
Steady State ◽  
Energy Metabolism ◽  
Metabolic Control Analysis ◽  
Steady States ◽  
Control Analysis ◽  
Top Down ◽  
Down Regulation ◽  
Metabolic Systems ◽  
And Control ◽  
Control Coefficients

This paper reviews top-down regulation analysis, a part of metabolic control analysis, and shows how it can be used to analyse steady states, regulation and homeostasis in complex systems such as energy metabolism in mitochondria, cells and tissues. A steady state is maintained by the variables in a system; regulation is the way the steady state is changed by external effectors. We can exploit the properties of the steady state to measure the kinetic responses (elasticities) of reactions to the concentrations of intermediates and effectors. We can reduce the complexity of the system under investigation by grouping reactions into large blocks connected by a small number of explicit intermediates-this is the top-down approach to control analysis. Simple titrations then yield all the values of elasticities and control coefficients within the system. We can use these values to quantify the relative strengths of different internal pathways that act to keep an intermediate or a rate constant in the steady state. We can also use them to quantify the relative strengths of different primary actions of an external effector and the different internal pathways that transmit its effects through the system, to describe regulation and homeostasis. This top-down regulation analysis has been used to analyse steady states of energy metabolism in mitochondria, cells and tissues, and to analyse regulation of energy metabolism by cadmium, an external effector, in mitochondria. The combination of relatively simple experiments and new theoretical structures for presenting and interpreting the results means that top-down regulation analysis provides a novel and effective way to analyse steady states, regulation and homeostasis in intricate metabolic systems.

scholarly journals Analysis and characterization of transition states in metabolic systems. Transition times and the passivity of the output flux

1991 ◽  
Vol 276 (1) ◽  
pp. 231-236 ◽  
Author(s):  
N V Torres ◽  
J Sicilia ◽  
E Meléndez-Hevia
Keyword(s):  
Steady State ◽  
Biological Significance ◽  
Transient State ◽  
Steady States ◽  
Transition Time ◽  
Enzyme Assays ◽  
Progress Curve ◽  
Metabolic Systems ◽  
Transition Times

In this paper we study the transitions between steady states in metabolic systems. In order to deal with this task we divided the total metabolite concentration at steady state, sigma, into two new fractions, delta (the Output Transition Time) and tau beta (Input Transition Time), which are related with the course of output and input mass to the system respectively. We show the equivalence time between these terms and the Total Transition Time, tau T, previously defined [Easterby (1986) Biochem. J. 233, 871-875]. Next, we define a new magnitude, the Output Passivity of a transition, rho, which quantifies a new aspect of the transition phase that we call the passivity of the output progress curve. With these magnitudes, all of them being experimentally accessible, several features of the transient state can be measured. We apply the present analysis to (a) the case of coupled enzyme assays, which allows us to reach conclusions about the progress curves in these particular transitions and the equivalence between tau sigma and tau delta, and (b) some experimental results that allow us to discuss the biological significance of the Output Passivity in the transition between steady states in metabolic systems.

scholarly journals Determination of control coefficients in intact metabolic systems

1994 ◽  
Vol 298 (2) ◽  
pp. 367-375 ◽  
Author(s):  
A Cornish-Bowden ◽  
J H S Hofmeyr
Keyword(s):  
Control Structure ◽  
Coefficient Matrix ◽  
High Accuracy ◽  
Kinetic Properties ◽  
State Variables ◽  
Metabolic System ◽  
Metabolic Systems ◽  
Complete Matrix ◽  
Control Coefficients

The control structure of a metabolic system can in principle be determined without the need for purification of the component enzymes and study of their kinetic properties, provided that their activities can be perturbed by amounts sufficient to produce measurable changes in the steady-state variables, i.e. the fluxes through the system and the concentrations of the intermediates. Each perturbation is characterized in terms of the co-response coefficients of all pairs of variables, i.e. the slopes of the lines produced when the logarithm of one variable is plotted against the logarithm of another, both varying in response to the same perturbation. If all the co-response coefficients are assembled into a matrix, the inverse of this matrix can be transformed into a matrix containing all the component elasticities, which can be inverted to provide the complete matrix of control coefficients. In a simple three-enzyme pathway studied, the analysis proves not to require unrealistically high accuracy in the original co-response measurements: even with errors with standard deviation +/- 5.77 degrees in the angles to the horizontal of the lines in the co-response plots (equivalent at best to errors of +/- 20% in the corresponding co-response coefficients), the final control coefficient matrix may be adequate for assessing the control structure of the system. Examination of literature data from studies of mitochondrial respiration and of gluconeogenesis indicates that considerably higher precision than this is achievable.

Estimation of steady-state flux rates in metabolic systems by computer simulations of radioactive tracer experiments

1993 ◽  
Vol 9 (5) ◽  
pp. 573-580
Author(s):  
Hermann-George Holzhütter ◽  
Anke Schwendel ◽  
Tilman Grune ◽  
Jörn Quedenau ◽  
Werner Siems
Keyword(s):  
Steady State ◽  
Computer Simulations ◽  
Radioactive Tracer ◽  
Steady State Flux ◽  
Metabolic Systems ◽  
Tracer Experiments

scholarly journals Control analysis applied to the whole body: control by body organs over plasma concentrations and organ fluxes of substances in the blood

1994 ◽  
Vol 297 (1) ◽  
pp. 115-122 ◽  
Author(s):  
G C Brown
Keyword(s):  
Steady State ◽  
Plasma Concentrations ◽  
Metabolic Control Analysis ◽  
The Body ◽  
Whole Body ◽  
Control Analysis ◽  
Physiological Control ◽  
Using Data ◽  
Control Coefficients

Metabolic control analysis is adapted as a method for describing and analysing the control by organs in the body over the fluxes and concentrations of substances carried in the blood. This physiological control analysis can most usefully be applied to substances with fluxes into and out of organs that are uniquely dependent only on their plasma concentrations. The organ flux of a substance is defined as the steady-state net flux of a substance into a particular organ. The organ flux control coefficients quantify the extent to which a particular organ controls the flux of a substance into the same or another particular organ. Organ concentration control coefficients quantify the extent to which an organ controls the steady-state concentration of a substance in the blood. The control coefficients are additive and obey summation, connectivity and branching theorems. Thus the control coefficients can be determined experimentally by measuring the sensitivities (elasticities) of organ fluxes to the plasma concentration of the substance. As an example of the application of these concepts, the control of ketone-body metabolism in vivo is analysed using data from the literature.

scholarly journals Endothelial glycocalyx degradation is associated with early organ impairment in polytrauma patients

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Feng Qi ◽  
Hao Zhou ◽  
Peng Gu ◽  
Zhi-He Tang ◽  
Bao-Feng Zhu ◽  
...  
Keyword(s):  
Injury Severity ◽  
Early Stage ◽  
Endothelial Glycocalyx ◽  
Control Group ◽  
Metabolic System ◽  
Metabolic Systems ◽  
Organ Systems ◽  
Severity Scores ◽  
Polytrauma Patients ◽  
Trauma Group

Abstract Background Endothelial glycocalyx (EG) abnormal degradation were widely found in critical illness. However, data of EG degradation in multiple traumas is limited. We performed a study to assess the EG degradation and the correlation between the degradation and organ functions in polytrauma patients. Methods A prospective observational study was conducted to enroll health participants (control group) and polytrauma patients (trauma group) at a University affiliated hospital between Feb 2020 and Oct 2020. Syndecan1 (SDC1) and heparin sulfate (HS) were detected in serum sample of both groups. In trauma group, injury severity scores (ISS) and sequential organ failure assessments (SOFA) were calculated. Occurrences of acute kidney injury (AKI), trauma-induced coagulopathy (TIC) within 48 h and 28-day all-cause mortality in trauma group were recorded. Serum SDC1 and HS levels were compared between two groups. Correlations between SDC1/HS and the indicators of organ systems in the trauma group were analyzed. ROC analyses were performed to assess the predictive value of SDC1 and HS for AKI, TIC within 48 h, and 28-day mortality in trauma group. Results There were 45 polytrauma patients and 15 healthy participants were collected, totally. SDC1 and HS were significantly higher in trauma group than in control group (69.39 [54.18–130.80] vs. 24.15 [13.89–32.36], 38.92 [30.47–67.96] vs. 15.55 [11.89–23.24], P <  0.001, respectively). Trauma group was divided into high degradation group and low degradation group according to SDC1 median. High degradation group had more severe ISS, SOFA scores, worse organ functions (respiratory, kidney, coagulation and metabolic system), and higher incidence of hypothermia, acidosis and shock. The area under the receiver operator characteristic curves (AUC) of SDC1 to predict AKI, TIC occurrence within 48 h and 28-day mortality were 0.838 (95%CI: 0.720–0.957), 0.700 (95%CI: 0.514–0.885) and 0.764 (95%CI: 0.543–0.984), respectively. Conclusions EG degradation was elevated significantly in polytrauma patients, and the degradation was correlated with impaired respiratory, kidney, coagulation and metabolic systems in early stage. Serum SDC1 is a valuable predictive indicator of early onset of AKI, TIC, and 28-day mortality in polytrauma patients.

Control analysis of photosynthetic sucrose synthesis: assignment of elasticity coefficients and flux-control coefficients to the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase

1989 ◽  
Vol 323 (1216) ◽  
pp. 327-338 ◽  
Keyword(s):  
Sucrose Phosphate Synthase ◽  
Control Analysis ◽  
Sucrose Synthesis ◽  
Flux Control ◽  
Fructose 1,6 Bisphosphatase ◽  
Flux Control Coefficients ◽  
Sucrose Phosphate ◽  
Control Coefficients ◽  
Phosphate Synthase

The use of elasticity coefficients and flux-control coefficients in a quantitative treatment of control is discussed, with photosynthetic sucrose synthesis as an example. Experimental values for elasticities for the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase are derived from their in vitro properties, and from an analysis of the in vivo relation between fluxes and metabolite levels. An empirical factor α , describing the response of the fructose 2,6-bisphosphate regulator cycle to fructose 6-phosphate is described, and an expression is derived relating α to the elasticities of the enzymes involved in this regulator cycle. The in vivo values for elasticities and α are then used in a modified form of the connectivity theorem to estimate the flux control coefficients of the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase during rapid photosynthetic sucrose synthesis.

scholarly journals COVID-19 infection and subsequent psychiatric morbidity, sleep problems and fatigue: analysis of an English primary care cohort of 226,521 positive patients

2021 ◽  
Author(s):  
Kathryn M Abel ◽  
Matthew J Carr ◽  
Darren M Ashcroft ◽  
Trudie Chalder ◽  
Carolyn A Chew-Graham ◽  
...  
Keyword(s):  
Primary Care ◽  
Sleep Problems ◽  
Psychiatric Morbidity ◽  
Negative Control ◽  
Control Analysis ◽  
Cox Proportional Hazard ◽  
Cox Proportional Hazard Models ◽  
Self Harm ◽  
Primary Hypothesis ◽  
Almost All

Objectives The primary hypothesis was that the risk of incident or repeat psychiatric illness, fatigue and sleep problems increased following COVID-19 infection. The analysis plan was pre-registered (https://osf.io/n2k34/). Design Matched cohorts were assembled using a UK primary care registry (the CPRD-Aurum database). Patients were followed-up for up to 10 months, from 1st February 2020 to 9th December 2020. Setting Primary care database of 11,923,499 adults (>16 years). Participants From 232,780 adults with a positive COVID-19 test (after excluding those with <2 years historical data or <1 week follow-up), 86,922 without prior mental illness, 19,020 with anxiety or depression, 1,036 with psychosis, 4,152 with fatigue and 4,539 with sleep problems were matched to up to four controls based on gender, general practice and year of birth. A negative control used patients who tested negative for COVID-19 and patients negative for COVID with an influenza diagnosis. Main Outcomes and Measures Cox proportional hazard models estimated the association between a COVID-19 positive test and subsequent psychiatric morbidity (depression, anxiety, psychosis, or self-harm), sleep problems, fatigue or psychotropic prescribing. Models adjusted for comorbidities, ethnicity, smoking and BMI. Results After adjusting for observed confounders, there was an association between testing positive for COVID-19 and almost all markers of psychiatric morbidity, fatigue and sleep problems. The adjusted hazard ratio (aHR) for incident psychiatric morbidity was 1.75 (95% CI 1.56-1.96). However, there was a similar risk of incident psychiatric morbidity for those with a negative COVID-19 test (aHR 1.57, 95% CI 1.51-1.63) and a larger increase associated with influenza (aHR 2.97, 95% CI 1.36-6.48). Conclusions There is consistent evidence that COVID-19 infection elevates risk of fatigue and sleep problems, however the results from the negative control analysis suggests that residual confounding may be responsible for at least some of the association between COVID-19 and psychiatric morbidity.

scholarly journals Improving the Antitumor Activity and Bioavailability of Sonidegib for the Treatment of Skin Cancer

Pharmaceutics ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1560
Author(s):  
Amr Gamal ◽  
Haitham Saeed ◽  
Fatma I. Abo El-Ela ◽  
Heba F. Salem
Keyword(s):  
Steady State ◽  
Skin Cancer ◽  
Entrapment Efficiency ◽  
The United States ◽  
Relative Bioavailability ◽  
Passive Targeting ◽  
Therapeutic Benefits ◽  
Steady State Flux

Throughout the United States and the world, skin cancer is the most frequent form of cancer. Sonidegib (SNG) is a hedgehog inhibitor that has been used for skin cancer treatment. However, SNG has low bioavailability and is associated with resistance. The focus of this work is to enhance bioavailability, anti-tumor efficacy and targeting of SNG via developing ethosome gel as a potential treatment for skin cancer. SNG-loaded ethosomes formulation was prepared and characterized in vitro by %entrapment efficiency (%EE), vesicle size, morphology, %release and steady-state flux. The results showed that the prepared formulation was spherical nanovesicles with a %EE of 85.4 ± 0.57%, a particle size of 199.53 ± 4.51 nm and a steady-state flux of 5.58 ± 0.08 µg/cm2/h. In addition, SNG-loaded ethosomes formulation was incorporated into carbopol gel to study the anti-tumor efficacy, localization and bioavailability in vivo. Compared with oral SNG, the formulation showed 3.18 times higher relative bioavailability and consequently significant anti-tumor activity. In addition, this formulation showed a higher rate of SNG penetration in the skin’s deep layers and passive targeting in tumor cells. Briefly, SNG-loaded ethosome gel can produce desirable therapeutic benefits for treatment of skin cancer.

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