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.

Kinetic Parameters of Continuous Flow Analysis

1967 ◽  
Vol 13 (6) ◽  
pp. 451-467 ◽  
Author(s):  
R E Thiers ◽  
R R Cole ◽  
W J Kirsch
Keyword(s):  
Steady State ◽  
Kinetic Parameters ◽  
Continuous Flow ◽  
Flow Analysis ◽  
Transient State ◽  
Steady States ◽  
Lag Phase ◽  
Time Interval ◽  
Base Line ◽  
Time Required

Abstract Unlike systems of batch analysis, continuous flow systems possess kinetic parameters. Associated with the steady state are such measurements as noise level and drift. This study reports on kinetic parameters associated with the transient state between the steady states including time required to change from base-line steady state to sample steady state and vice versa, characteristics of this change, time interval between samples, proportionality of sampling and washing time, fraction of steady state reached in any given sampling time, and interaction between samples. The transition between steady states has been found to obey first order kinetics to a good first approximation. This observation enables correlation of all of the above listed properties in quantitative fashion using new characteristic constants for continuous flow-the half-wash time (W1/2) and the lag phase time (L). These parameters, well known in other contexts such as radioactivity, can be employed as "figures of merit" for any continuous flow system or component, can be utilized to calculate performance characteristics, and are useful in evaluating and optimizing over-all performance.

Steady-state kinetics

2000 ◽  
Author(s):  
Athel Cornish-Bowden
Keyword(s):  
Steady State ◽  
Enzyme Kinetics ◽  
Single Molecule ◽  
Transient State ◽  
Curve Analysis ◽  
Rate Equations ◽  
Progress Curve ◽  
Steady State Kinetics ◽  
Time Regime ◽  
Time Courses

All of chemical kinetics is based on rate equations, but this is especially true of steady-state enzyme kinetics: in other applications a rate equation can be regarded as a differential equation that has to be integrated to give the function of real interest, whereas in steady-state enzyme kinetics it is used as it stands. Although the early enzymologists tried to follow the usual chemical practice of deriving equations that describe the state of reaction as a function of time there were too many complications, such as loss of enzyme activity, effects of accumulating product etc., for this to be a fruitful approach. Rapid progress only became possible when Michaelis and Menten (1) realized that most of the complications could be removed by extrapolating back to zero time and regarding the measured initial rate as the primary observation. Since then, of course, accumulating knowledge has made it possible to study time courses directly, and this has led to two additional subdisciplines of enzyme kinetics, transient-state kinetics, which deals with the time regime before a steady state is established, and progress-curve analysis, which deals with the slow approach to equilibrium during the steady-state phase. The former of these has achieved great importance but is regarded as more specialized. It is dealt with in later chapters of this book. Progress-curve analysis has never recovered the importance that it had at the beginning of the twentieth century. Nearly all steps that form parts of the mechanisms of enzyme-catalysed reactions involve reactions of a single molecule, in which case they typically follow first-order kinetics: . . . v = ka . . . . . . 1 . . . or they involve two molecules (usually but not necessarily different from one another) and typically follow second-order kinetics: . . . v = kab . . . . . . 2 . . . In both cases v represents the rate of reaction, and a and b are the concentrations of the molecules involved, and k is a rate constant. Because we shall be regarding the rate as a quantity in its own right it is not usual in steady-state kinetics to represent it as a derivative such as -da/dt.

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.

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 An Electrochemical Approach to Follow and Evaluate the Kinetic Catalysis of Ricin on hsDNA

Life ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 405
Author(s):  
George Oliveira ◽  
José Maurício Schneedorf
Keyword(s):  
Catalytic Efficiency ◽  
Ricin Toxin ◽  
Wave Voltammetry ◽  
Progress Curve ◽  
Electrochemical Approach ◽  
Electro Oxidation ◽  
Castor Seeds ◽  
Identification And Characterization ◽  
Medical Countermeasures

International authorities classify the ricin toxin, present in castor seeds, as a potential agent for use in bioterrorism. Therefore, the detection, identification, and characterization of ricin are considered the first actions for its risk assessment during a suspected exposure, parallel to the development of therapeutic and medical countermeasures. In this study, we report the kinetic analysis of electro-oxidation of adenine released from hsDNA by the catalytic action of ricin by square wave voltammetry. The results suggest that ricin-mediated adenine release exhibited an unusual kinetic profile, with a progress curve controlled by the accumulation of the product and the values of the kinetic constants of 46.6 µM for Km and 2000 min−1 for kcat, leading to a catalytic efficiency of 7.1 × 105 s−1 M−1.

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