Hemoglobin allosteric change

Hemoglobin functions efficiently to meet these requirements. It does so through its allosteric transition between structurally different high-affinity and low-affinity states. Carbon dioxide, protons, and other substances all affect hemoglobin and promote allosteric changes. 

Models of Allosteric Change in Hemoglobin (Figure 7.10, Figure 7.12)... 

A Closer Look at the Allosteric Change in Hemoglobins (Figure 7.13, Figure 7.14,... 

Xu, C., Tobi, D., Bahar, I. Allosteric changes in protein structure computed by a simple mechanical model hemoglobin T R2 transition, J. Mol. Biol. 2003,333,153. 

FIGURE 6-29 Substrate-activity curves for representative allosteric enzymes. Three examples of complex responses of allosteric enzymes to their modulators, (a) The sigmoid curve of a homotropic enzyme, in which the substrate also serves as a positive (stimulatory) modulator, or activator. Note the resemblance to the oxygen-saturation curve of hemoglobin (see Fig. 5-12). (b) The effects of a positive modulator (+) and a negative modulator (—) on an allosteric enzyme in which K0 5 is altered without a change in Zmax. The central curve shows the substrate-activity relationship without a modulator, (c) A less common type of modulation, in which Vmax is altered and /C0.sis nearly constant. 

In addition, allosteric enzymes may be controlled by effector molecules (activators and inhibitors) that bind to the enzyme at a site other than the active site (either on the same subunit or on a different subunit), thereby causing a change in the conformation of the active site which alters the rate of enzyme activity (cf. the binding of C02, H+ and 2,3-bisphosphoglycerate to hemoglobin see Topic B4). An allosteric activator increases the rate of enzyme activity, while an allosteric inhibitor decreases the activity of the enzyme. 

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