Biochemical reactions steady state condition

Stoichiometric analysis goes beyond topological arguments and takes the specific physicochemical properties of metabolic networks into account. As noted above, based on the analysis of the nullspace of complex reaction networks, stoichiometric analysis has a long history in the chemical and biochemical sciences [59 62]. At the core of all stoichiometric approaches is the assumption of a stationary and time-invariant state of the metabolite concentrations S°. As already specified in Eq. (6), the steady-state condition... 

This simple example may be generalized to biochemical reaction cycles in which there are a number of reactions and boundary flows that add and remove substrates. The controlled concentrations and boundary flows maintain the system in a nonequilibrium steady-state condition. 

The specific features of voltammetry at microelectrodes (absence of interferences arising from charging currents, uncompensated resistance and instrumental imperfections, high signal/noise ratio) were emphasized in chapter 2 (section 2.3) of this volume. Various construction modes and application of (ultra)-microelectrodes in chemical and biochemical practice will be treated in chapter 7 of this volume. In this subsection the exploitation of microelectrodes (under steady-state conditions) to investigation of electrode mechanisms and homogeneous reaction kinetics is discussed. 

Most chemically reacting systems tliat we encounter are not tliennodynamically controlled since reactions are often carried out under non-equilibrium conditions where flows of matter or energy prevent tire system from relaxing to equilibrium. Almost all biochemical reactions in living systems are of tliis type as are industrial processes carried out in open chemical reactors. In addition, tire transient dynamics of closed systems may occur on long time scales and resemble tire sustained behaviour of systems in non-equilibrium conditions. A reacting system may behave in unusual ways tliere may be more tlian one stable steady state, tire system may oscillate, sometimes witli a complicated pattern of oscillations, or even show chaotic variations of chemical concentrations. 

Much of the chemistry of the oceans and of freshwater systems depends on the kinetics of various physical and chemical processes and on biochemical reactions rather than on equilibrium conditions. The simplest model describing systems open to their environment is the time-invariant steady-state model. Because the sea has remained constant for the recent geological past, it may be well justified to interpret the ocean in terms of a steady-state model. 

Under appropriate conditions and given sufficient time, individual biochemical reactions carried out In a test tube eventually will reach equilibrium. Within cells, however, many reactions are linked In pathways In which a product of one reaction serves as a reactant In another or Is pumped out of the cell. In this more complex situation, when the rate of formation of a substance Is equal to the rate of Its consumption, the concentration of the substance remains constant, and the system of linked reactions for producing and consuming that substance Is said to be In a steady state (Figure 2-21). One consequence of such linked reactions Is that they prevent the accumulation of excess Intermediates, protecting cells from the harmful effects of Intermediates that have the potential of being toxic at high concentrations. 

The data and associated model fits used to obtain these kinetic constants are shown in Figures 4.10 through 4.12. These data on quasi-steady reaction flux as functions of reactant and inhibitor concentrations are obtained from a number of independent sources, as described in the figure legends. Note that the data sets were obtained under different biochemical states. In fact, it is typical that data on biochemical kinetics are obtained under non-physiological pH and ionic conditions. Therefore the reported kinetic constants are not necessarily representative of the biochemical states obtained in physiological systems. 

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