Substrate binding cooperative

V2 shows a positive substrate binding cooperativity in this reaction and also a positive kinetic cooperativity in regard to adenine (see Figure 4). 

The kinetic cooperativity can be distinguished from the substrate binding cooperativity (spatial cooperativity by means of homotropic interactions) by means of binding studies, measurements of the initial speed and the determination of the type of conformation (9,12). 

In the case of the oligomeric enzymes the kinetic cooperativity is more complex. The interactions between the subunits can influence the rate (speed) of the transition or even alter the three-dimensional structure of the subunits themselves. Weakly coupled subunits generate no sigmoidal substrate saturation curve and in this instance the kinetic cooperativity can be greater or smaller than the corresponding substrate binding cooperativity. This is the case for V2, as it can be seen from the values of h exf(13)-... 

Negative substrate binding cooperativity of the enzyme for dT (Figure 5a). The value... 

Positive substrate binding cooperativity for thymidine (Eigure 5c). 

Adenine is a negative, allosteric effector for the enzyme and at the same time also an effector of the cooperativity of V2 for thymidine. The originally negative substrate binding cooperativity of the enzyme for thymidine is transformed into a positive one. 

No kinetic cooperativity was able to be determined against thymidine. The Hill coefficients characterizing the substrate binding cooperativity are h = 0.135 (at 0.07 mM adenine) and h = 1.49 (at 1.0 mM adenine). 

Muscle Glycogen Phosphorylase Shows Cooperativity in Substrate Binding... 

A linear form of the Hill equation is used to evaluate the cooperative substrate-binding kinetics exhibited by some multimeric enzymes. The slope n, the Hill coefficient, reflects the number, nature, and strength of the interactions of the substrate-binding sites. A... 

A prerequisite for this model is the existence of both external and internal gates, i.e., protein domains that are capable of occluding access to the substrate binding site from the extracellular and intracellular environment, respectively. Little is known about such domains in this family of transporters. The molecular mechanisms governing the cooperative function of the putative gating domains also remain unknown. It could be predicted, however, that stabilization of the transporter in the outward-facing conformation in the absence of substrate but in the presence of Na+ requires a network of con-... 

Enzymes may exist as simple monomers, or as homo- or heterodimers, or as multimers. In multimeric enzymes, each component monomer may possess a catalytic site alternatively, the catalytic site may be located at the interface between two or more monomers, or only one monomer of a heteromultimer may possess an active site. It is not uncommon in dimeric or multimeric enzymes containing two or more active sites for some degree of cooperativity to exist between the sites, with respect to the substrate binding or substrate turnover number (Monod et ah, 1965). 

In a series of papers, we have proposed the torsional mechanism of energy transduction and ATP synthesis, the only unified and detailed molecular mechanism of ATP synthesis to date [16-20,56] which addresses the issues of ion translocation in Fq [16, 20, 56], ionmotive torque generation in Fq [16, 20, 56], torque transmission from Fq to Fj [17,18], energy storage in the enzyme [17], conformational changes in Fj [18], and the catalytic cycle of ATP synthesis [18, 19]. We have also studied the thermodynamic and kinetic aspects of ATP synthesis [19,20,41,42,56]. A kinetic scheme has been developed and mathematically analyzed to obtain a kinetic model relating the rate of ATP synthesis to pHjn and pH m in the Fq portion and the adenine nucleotide concentrations in the Fj portion of ATP synthase. Analysis of these kinetic models reveals a wealth of mechanistic details such as the absence of cooperativity in the Fj portion of ATP synthase, order of substrate binding and product release events, and kinetic inequivalence of ApH and Aip. 

ATP + (d)CMP = ADP + (d)CDP (<4> formation of a ternary complex, addition of substrates is random [5] <1> reaction proceeds by a sequential mechanism, a ternary complex of the enzyme with both substrates is formed as the central intermediate in the reaction [12] <3> reaction mechanism is sequential and nonequilibrium in nature, substrates bind to the enzyme in a random order, substrate binding is cooperative [14] <7> the mechanism is analogous to the phosphoryl transfer mechanism in cAMP-dependent protein kinase that phosphorylates the hydroxyl groups of serine residues [16] <8> random bi-bi mechanism [17])... 

In the presence of CTP the binding of the substrates is cooperative, as would be anticipated if there is a two-state conformational equilibrium involving the catalytic subunits. This would be similar to the case depicted in Fig. 9-13 except that trimers rather than dimers are involved and the inhibitor is a part of the regulatory subunit and is controlled by binding of CTP. 

ATP is both a substrate and an inhibitor of the enzyme phosphofructokinase (PFK). Although the substrate fructose-6-phosphate binds cooperatively to the active site, ATP does not bind cooperatively. Explain how ATP may be both a substrate and an inhibitor of PFK. 

Furthermore, in 33 the receptor is built from two protonated tripodal subunits of the tren type, N(CH2CH2NH2)3, located at each pole of the molecule, which cooperate in substrate binding. This is a feature of coreceptor molecules, which will be discussed below (Chapter 4). 

A successive report from the same group [50] discussed the influence of molecular recognition on the substrate binding, and therefore catalytic activity, in the peroxidase system previously developed. The authors reached the conclusion that the haemin played a role not only in the catalytic cycle but it was also essential in the molecular recognition of the substrate, by cooperating with the other co-monomers, 4-vinyl-pyridine and acrylamide. Moreover, imprinting efficiency was demonstrated by showing that the catalytic activity of the MIP was enhanced 7.6 times with respect to the NIP. 

Several pharmaceutical enzymes belong to the group of serine-histidine estero-proteolytic enzymes (serine proteases), which display their catalytic activity with the aid of an especially reactive serine residue, whoso p-hydroxyi group forms a covalent bond with the substrate molecule. This reaction takes place by cooperation with the imidazole base of histidine. The specificity of the enzymes is achieved by the characteristic strocture of their substrate-binding centers, which in these proteases are built according to the same principle. They consist of a hydrophobic slit formed by apolar aide chains of amino acids and a dissociated side chain-located carboxyl group of an aspartic add residue at the bottom. 

Essentially, a-chymotrypsin has these characteristics the selectivity in the substrate binding, the charge-relay system in the active center and a contribution of the bound substrate to the catalysis, as cooperativities. 

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