Enzyme processes do not display any apparent “finality” when considered
isolated, however they do within the cell. In fact the global behavior of the cell relies
upon a co-ordination of many enzyme reactions. The aim of the so-called “metabolic
control theory” is to show how many enzyme reactions are connected as to form a
coherent network that possesses properties that are quantitatively and qualitatively
different from those of individual enzyme reactions. The concept of “cascade” is
discussed in this Chapter and their properties are shown to be different from those of the
same enzymes considered in isolation. Many enzymes within the cell are associated
with cell structures that behave as polyanions. Electrostatic repulsion of negatively
charged substrates by the negative charges of plant cell wall generates an apparent
negative co-operativity of enzyme reactions that take place in the cell wall. These
effects can be modulated by external ionic strength. It follows that the behavior of
enzymes in the cell have properties quite different from the same enzymes in free
solution.
Keywords: Metabolic control theory, Parameters of a metabolic process,
Summation theorems, Homogeneous functions, Elasticity of an enzyme reaction,
Enzyme cascades, Electrostatic partitioning of ions, Enzymes and electrostatic
partitioning, Donnan equation, Bound-enzyme activity and heterogeneously
charged matrices, Enzyme activity and heterogeneously charged matrices,
Enzyme co-operativity and complexity of charged matrices, Enzymes and plant
cell wall extension.
