Biochemical kinetics

The concentration of the enzyme-substrate complex influences the velocity of enzymatic reactions. The relationship between the velocity of a reaction and the concentration of substrates is described by the Michaelis-Menton equation  

Order of reaction. At very high substrate concentrations [S] K, the velocity of reaction is essentially independent of the substrate concentration. The velocity is constant and equal to The rate of reaction is a zero-order reaction. At very low substrate concentrations 

Activation energy. The minimum energy required to carry out the reaction is called the energy of activation, E. If a reaction requires higher activation energy, the rate of reaction is lowered. The presence of a catalyst lowers the activation energy and increases the rate of reaction. In biological systems, enzymes act as catalysts. 

Arrhenius equation. Explains the relationship between the rate constant of a reaction, k, and the activation energy, E  

The effect of temperature on the rate of reaction is frequently expressed in terms of a temperature coefficient, Q q, which is the factor by which the rate of reaction increases when the temperature is raised by 10°C. 

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As with the Langmuir adsorption isotherm, which in shape closely resembles Michaelis-Menten type biochemical kinetics, the two notable features of such reactions are the location parameter of the curve along the concentration axis (the value of Km or the magnitude of the coupling efficiency factor) and the maximal rate of the reaction (Vmax). In generic terms, Michaelis-Menten reactions can be written in the form... 

As we described in Chapter 3, the binding of reversible inhibitors to enzymes is an equilibrium process that can be defined in terms of the common thermodynamic parameters of dissociation constant and free energy of binding. As with any binding reaction, the dissociation constant can only be measured accurately after equilibrium has been established fully measurements made prior to the full establishment of equilibrium will not reflect the true affinity of the complex. In Appendix 1 we review the basic principles and equations of biochemical kinetics. For reversible binding equilibrium the amount of complex formed over time is given by the equation... 

The preceding accomplishments are applied in nature, but required tremendous amounts of basic research on mass transfer, interactions of materials with biological components, fluid dynamics, separation processes (especially chromatography and membrane separations), and biochemical kinetics. 

Most problems associated with approximate kinetics are avoided when Michaelis Menten-type rate equations are utilized. Though this choice sacrifices the possibility of analytical treatment, reversible Michaelis Menten-type equations are straightforwardly consistent with fundamental thermodynamic constraints, have intuitively interpretable parameters, are computationally no more demanding than logarithmic functions, and are well known to give an excellent account of biochemical kinetics. Consequently, Michaelis Menten-type kinetics are an obvious choice to translate large-scale metabolic networks into (approximate) dynamic models. It should also be emphasized that simplified Michaelis Menten kinetics are common in biochemical practice almost all rate equations discussed in Section III.C are simplified instances of more complicated rate functions. 

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