Conformation change allosteric phenomena

The multifunctional enzyme V2 is (like the enzymes VI and V3) a regulatory (allosteric) and indeed a hysteretic (8) and, more precisely, a mnemonic enzyme. Hysteresis (kinetic cooperativity or chronological cooperativity) (9) is the phenomenon of slow conformational changes of enzymes by isomerization, association-dissociation or by the binding of an effector. 

Some comments are required on effectors which are of importance in metabolic and other regulation phenomena. The term allosteric inhibition was introduced by Monod, Changeux Jacob (1963) to explain the discovery of feedback inhibitors, which are competitive with the substrate but not closely structurally related to it. Such inhibitors were called allosteric in contrast to the usual competitive inhibitors which are isosteric with the substrate to fit competitively into the same binding site. Allosteric competitive inhibition occurs at a site (allosteric site) which is separate from the substrate binding sites. Conununication between these separate sites about respective occupancy occurs through conformation changes and these are transmitted through subunit interfaces. The term was extended to the related control phenomenon of allosteric activation, which occurs when a metabolite binds to an allosteric site and decreases the for... 

Not all enzymes show the simple hyperbolic dependence of rate of reaction on substrate concentration shown in Figure 2.8. Some enzymes consist of several separate protein chains, each with an active site. In many such enzymes, the binding of substrate to one active site causes changes in the conformation not only of that active site, but of the whole multi-subunit array. This change in conformation affects the other active sites, altering the ease with which substrate can bind to the other active sites. This is cooperativity — the different subunits of the complete enzyme cooperate with each other. Because there is a change in the conformation (or shape) of the enzyme molecule, the phenomenon is also called allostericity (from the Greek for different shape ), and such enzymes are called allosteric enzymes. 

---