Cooperative allosteric interactions

The simplest model that can describe allosteric interactions at GPCRs is the ternary complex allosteric model [9], As shown in Figure 1, according to this model two parameters define the actions of allosteric agent (X) its affinity for the unoccupied receptor (Kx) and its cooperativity (a) with the ligand (A) that interacts at the primary binding site a < 1 represents negative cooperativity a = 1, no cooperativity a > 1, positive cooperativity. 

In the following, we mainly use variants of the functional form given in Eq. (56) to describe cooperativity and allosteric regulation in metabolic systems. In particular, within Section VII.C, we discuss a general functional form of rate equations, including allosteric interaction... 

Ca2+. The highly cooperative opening of calcium channels by nanomolar concentrations of IP enables cells to detect and amplify very small changes in the concentration of this messenger. The cooperativity of IP3 binding and channel opening is another example of the role of allosteric interactions. 

The first coordination shell of Fe in Fib is identical to that of Mb, but there are other major differences that influence the spectroelectrochemical/Nernst plot profile of Hb and make it distinct from that of Mb. Hb is a tetrameric protein with four heme-containing subunits (a2p2), each of which is redox-active. Differences between Mb and Hb include amino-acid sequence, which results in different redox potentials for the a and (3 chains, plus subunit-subunit interactions that lead to allostery in Hb. This allosteric interaction leads to cooperative electron transfer that gives rise to a non-Nernstian redox profile that requires special consideration for data analysis and interpretation of results. ... 

A similar system has been used to study the influence of allosteric interactions on cyanide dissociation in hemoglobin (112). The results of these RSSF studies demonstrate that the cyanide complex of the a- and 3-chains are spectroscopically distinguishable and that dissociation is a cooperative process that is modulated by allosteric effectors. 

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). 

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