Allosteric behavior

A model for the allosteric behavior of hemoglobin is based on recent observations that oxygen is accessible only to the heme groups of the a-chains when hemoglobin is in the T conformational state. Perutz has pointed out that the heme environment of /3-chains in the T state is virtually inaccessible because of steric hindrance by amino acid residues in the E helix. This hindrance dis-... 

Allosteric behavior in cytochrome p450-dependent in vitro drug-drug interactions a prospective based on conformational dynamics. Chemical Research in Toxicology, 14 (4), 338-347. 

Allosteric behavior of the heterotropic variety is seen in the interaction between polymer and detergent or polymer and polymer (Shirahama, 1974 Arai et al., 1973 Tsuchida and Osada, 1973). Shinkai et al. (1977b) observed a sigmoid profile of rate constant vs. concentration of cationic detergents in the acyl transfer reaction from p-nitrophenyl acetate (PNPA) to copolymers (7). 

When an enzyme reacts to effectors (substrates, activators, or inhibitors) with conformational changes that increase or reduce its activity, it is said to show allosteric behavior (see p. 116). Allosteric enzymes are usually oligomers with several subunits that mutually influence each other. 

Shirmer, T. Evans, P.R. (1990) Structural basis for the allosteric behavior of phosphofructokinase. Nature 343, 140-145. 

Allosteric behavior in a ditopic cavitand receptor has been induced via metal coordination [62]. Addition of Ag+ ions to a solution of a 2,2 -bipyridine-bridged biscavitand 56 switches the molecule from an S-shaped to a C-shaped conformation with the two cavities facing each other. At the same time two bis-cavitand molecules are brought together to give an overall tetratopic complex 57 (Figure 7.24). 

Furthermore, the reconstituted enzyme has the same allosteric properties as the native enzyme. Thus, ATCase is composed of discrete catalytic and regulatory suhunits, which interact in the native enzyme to produce its allosteric behavior. 

One of the basic assumptions of the concerted model of the allosteric behavior of proteins is that in the absence of ligand ... 

The effect of specific phospholipid molecules on overall protein conformation and hence activity may be considered as an example of allostericity. Such allosteric behavior has been discussed in terms of a second phospholipid-binding site or as discrete interactions between the head groups of phospholipids and specific residues on the interfacial binding surface of the enzyme. The emerging evidence for sPLAjS supports a model involving multiple interactions between enzyme and interfacial lipid [8]. 

Multistate models Neither the KNF nor the MWC model exactly explains the allosteric behavior of proteins, including hemoglobin. Consequently, more complex models have been devised. Most such models retain the MWC concept of a concerted switch in conformation but involve more than two states for the entire molecule. 

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