Kinetic structure of a biochemical pathway

Many enzymes in the cell are organised into sequences, so that the reactions they catalyse are integrated into pathways or processes. In these pathways, a precursor or substrate is converted to a product, e.g. glucose is converted to lactic acid amino acids are polymerised to form protein glutamine is converted to aspartate. These pathways have both a thermodynamic and a kinetic structure. The thermodynamic structure is presented in Chapter 2. The kinetic structure is described here. There are three basic facts that must be appreciated before the kinetic structure is explained. 

A reaction in a metabolic pathway is likely to be nonequilibrium if the maximum catalytic activity of the enzyme that catalyses the reaction is low in comparison with those of other enzymes in the pathway. In consequence, the concentration of substrate of this reaction is likely to be high whereas that of the product is likely to be low, since the next enzyme in the sequence readily catalyses its removal. Because the concentration of this product is low, the rate of the reverse component of the reaction is very much less than the rate of the forward component. This situation characterises a non-equilibrium process. Conversely, a reaction is near-equiUbrium if the maximum catalytic activity of the enzyme is high in relation to those of other enzymes in the pathway in this case, the rates of the forward and the reverse components of the reaction are similar and both are much greater than the overall flux 

Well-known examples of enzyme deficiency diseases include  

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