Allosteric Cooperativity

NUCLEATION COOPERATIVITY ALLOSTERISM HYSTERESIS JENKINS MECHANISM JOB PLOT... 

COOPERATIVITY ALLOSTERISM INDUCED FIT MODEL MONOD-WYMAN-CHANGEUX MODEL INDEPENDENT BINDING LINKED FUNCTIONS ADAIR EQUATION POSITIVE COOPERATIVITY NEGATIVE COOPERATIVITY KOSMOTROPES CHAOTROPIC AGENTS HOFMEISTER SERIES Kp, Kq, K .. . ... 

In hemoglobin, four similar units are connected in a tetramer by hydrophobic interactions. Binding of the first oxygen atom enhances the binding constants of the three remaining units. For such cooperative ( allosteric ) effects, which are typical for biological but out of reach for synkinetic systems, the reader is referred to biochemistry textbooks (Dickerson and Geis, 1969,1983 Voets, 1990). 

The nonlinearity of kinetic equations of the Hodgkin-Huxley type might also result, at least in part, from the cooperative allosteric properties of ion channels. The crystallographic study of these channels indeed reveals that they are often formed by multiple interacting subunits (Noda et al, 1984). 

In the concerted model, the effects of inhibitors and activators can also be considered in terms of shifting the equilibrium between the T and R forms of the enzyme. The binding of inhibitors to allosteric enzymes is cooperative allosteric inhibitors bind to and stabilize the T form of the enzyme. The binding of activators to allosteric enzymes is also cooperative allosteric activators bind to and stabilize the R form of the enzyme. When an activator, A, is present, the cooperative binding of A shifts the equilibrium between the T and R forms, with the R form favored (Figure 7.6). As a result, there is less need for substrate, S, to shift the equilibrium in favor of the R form, and less cooperativity in the binding of S is seen. 

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