Cooperativity and Hysteresis

Experimental experience demonstrates that in any case large reaction dipole moments AM) are required to produce major displacements of dipolar equilibria high ionic valencies are necessary for larger dissociation field effects in ionic association-dissociation reactions/  

These conditions generally require that the reaction partners themselves have either large dipole moments or large polarizabilities or a high density of fixed ionic groups. The structures which fulfill these conditions are macromolecules and macromolecular organizations such as polyionic biopolymers, biopolymer complexes, or biomembranes. 

In a cooperative process, a larger sequence of residues in a polymer chain or an entire subunit (domain) of a macromolecular system are the reaction units which transform as a whole. Returning to dipolar systems, even if the dipole moment of a single residue in such a sequence is small, the total cooperative unit may have a very large dipole moment. In this manner, cooperativity sums small reaction moments of elementary steps into concerted action it thus represents a powerful amplification mechanism. 

If a cooperative chemical transformation is coupled to an electric field effect, a relatively small change of the field intensity may suffice to cause a practically complete transition. Thus, electrical chemical coupling amplified by cooperativity is probably also a powerful mechanism for a direct and very efficient electrical control of biochemical reactivity. This principle is certainly very suggestive for the exploration of bioelectric mechanisms in general. 

It is well known that in certain cases the occurrence of structural 

---

There is almost no biochemical reaction in a cell that is not catalyzed by an enzyme. (An enzyme is a specialized protein that increases the flux of a biochemical reaction by facilitating a mechanism [or mechanisms] for the reaction to proceed more rapidly than it would without the enzyme.) While the concept of an enzyme-mediated kinetic mechanism for a biochemical reaction was introduced in the previous chapter, this chapter explores the action of enzymes in greater detail than we have seen so far. Specifically, catalytic cycles associated with enzyme mechanisms are examined non-equilibrium steady state and transient kinetics of enzyme-mediated reactions are studied an asymptotic analysis of the fast and slow timescales of the Michaelis-Menten mechanism is presented and the concepts of cooperativity and hysteresis in enzyme kinetics are introduced. 

---