Complex ternary

The catalytic subunit of cAPK contains two domains connected by a peptide linker. ATP binds in a deep cleft between the two domains. Presently, crystal structures showed cAPK in three different conformations, (1) in a closed conformation in the ternary complex with ATP or other tight-binding ligands and a peptide inhibitor PKI(5-24), (2) in an intermediate conformation in the binary complex with adenosine, and (3) in an open conformation in the binary complex of mammalian cAPK with PKI(5-24). Fig.l shows a superposition of the three protein kinase configurations to visualize the type of conformational movement. 

Fig. 2. Conformational free energy of closed, intermediate and open protein kinase conformations. cAPK indicates the unbound form of cAMP-dependent protein kinase, cAPKiATP the binary complex of cAPK with ATP, cAPKiPKP the binary complex of cAPK with the peptide inhibitor PKI(5-24), and cAPK PKI ATP the ternary complex of cAPK with ATP and PKI(5-24). Shown are averaged values for the three crystal structures lATP.pdb, ICDKA.pdb, and ICDKB.pdb. All values have been normalized with respect to the free energy of the closed conformations.

In summary, ligands tend to diminish the affinity of the substrate for the Lewis-acid catalyst as well as the extent of activation by this catalyst, once the ternary complex is formed. Only a few examples of ligand-accelerated catalysis " have been described... 

Table 3.1 summarises the influence of the diamine ligands on the equilibrium constant for binding of 3.8c to the ligand-metal ion complex (K ) and the second-order rate constant for reaction of the ternary complex (ICjat) (Scheme 3.5) with diene 3.9. 

Interestingly, the rate constants for Diels-Alder reaction of the ternary complexes with 3.9 are remarkably similar. Only with 2,2 -bipyridine and 1,10-phenanthroline as ligands, a significant change in reactivity is observed. It might well be that the inability of these complexes to adopt a planar geometry hampers the interaction between the copper ion and the dienophile, resulting in a decrease of the rate of the catalysed Diels-Alder reaction. 

Recent investigation of the effect of substituents in the para position of the phenylalanine ligand on the stability of the ternary complexes has revealed the secpience Br > OH > Q NH2 > H > F". Interestingly, analysis of CD spectra indicates a reduction of the arene-arene interaction" upon addition of 1,4-dioxane to aqueous solutions of the mixed-ligand complexes, in disagreement with previous observations by Sigel" . 

Amino-5 -deoxy-2, 3 -0-isopropylideneadenosine was acylated at N-5 with an activated derivative of the 6-carboxy-2-naphthyl ester of Kemp s acid imide. The resulting molecule possesses self-complementary binding sites, the key feature of replicating molecules that act as templates for their own reproduction. The dimer of this molecule is, however, not very stable K = 630 L mol ). When the two initially mentioned educts are added, a small proportion of the ternary complex is also formed and undergoes a fast, template-catalysed... 

PVSA-SG film was used for determination of Fe(Phen) + and Zn + as ternary complex Zn +-Phen-bengal rose by spectrophotometric method. The calibration graph was linear in the concentration 5T0 -5T0 mol/lfor Fe(II) and FlO - 5T0 mol/1 for Zn(II). The film can be regenerated and reused. LG-PDMDA-SG film was shown to be perspective modificator of the PG electrode surface and used for voltammetric detection of Mo(VI) at ppb level. 

It was shown that Zn + adsorbed onto SG-PVSA composite film as Zn(Phen) complex. It can be detected spectrophotometrically after treatment with anionic dye Bengal Rose (BR). Ternary complex Zn + - Phen-BR formed on the surface under optimal conditions. SG-PVSA film was used for determination of Zn + by spectrophotometric method. The calibration graph was linear in the concentration range 2,5T0 - STO mol/l. 

The opportunity of use of a ternary complex of ions Eu(III) with oxatetracycline (OxTC) and citrat-ions (Cit) for luminescent detection of OxTC in milk after chromatographic isolation is shown. 

SPECTROFLUORIMETRIC DETERMINATION OF OXYTETRACYCLINE AND CITRATE ION USING TERNARY COMPLEX WITH EUROPIUM(III)... 

We detenuined the influence of oxy- and ketocarboxylic acids (succinate, fumarate, adipinate, a-ketoglutarate, isocitrate, tartrate, E-malate) on the luminescence intensity of the Eu-OxTc complex. These substances interact as polydentate ligands similarly to citrate with the formation of ternary complexes with Eu-OxTc. As to succinate, fumarate, adipinate and a-ketoglutarate this they cannot effectively coordinate with EiT+ and significant fluorescence enhancement was not observed. 

TFIIA and TFIIB are two basal transcription factors that are involved in the nucleation stages of the preinitiation complex by binding to the TBP-TATA box complex. Crystal structures of the ternary complex TFIIA-TBP-TATA box have been determined by the groups of Paul Sigler, Yale University, and Timothy Richmond, ETH, Zurich, and that of the TFIIB-TBP-TATA box by Stephen Burley and collaborators. The TBP-DNA interactions and the distortions of the DNA structure are essentially the same in these ternary complexes as in the binary TBP-TATA complex. 

Nikolov, D.B., et al. Crystal structure of a TFllB-TBP-TATA-element ternary complex. Nature 377 119-128, 1995. 

The first possibility envisages essentially the same mechanism as for the second-order process, but with Bt2 replacing solvent in the rate-determining conversion to an ion pair. The second mechanism pictures Bt2 attack on a reversibly formed ion-pair intermediate. The third mechanism postulates collide of a ternary complex tiiat is structurally similar to the initial charge-transfer complex but has 2 1 bromine alkene stoichiometry. There are very striking similarities between the second-order and third-order processes in terms of magnitude of p values and product distribution. In feet, there is a quantitative correlation between the rates of the two processes over a broad series of alkenes, which can be expressed as... 

The overall direction of the reaction will be determined by the relative concentrations of ATP, ADP, Cr, and CrP and the equilibrium constant for the reaction. The enzyme can be considered to have two sites for substrate (or product) binding an adenine nucleotide site, where ATP or ADP binds, and a creatine site, where Cr or CrP is bound. In such a mechanism, ATP and ADP compete for binding at their unique site, while Cr and CrP compete at the specific Cr-, CrP-binding site. Note that no modified enzyme form (E ), such as an E-PO4 intermediate, appears here. The reaction is characterized by rapid and reversible binary ES complex formation, followed by addition of the remaining substrate, and the rate-determining reaction taking place within the ternary complex. 

In this case, the leading substrate, A (also called the obligatory or compulsory substrate), must bind first. Then the second substrate, B, binds. Strictly speaking, B cannot bind to free enzyme in the absence of A. Reaction between A and B occurs in the ternary complex, and is usually followed by an ordered release of the products of the reaction, P and Q. In the schemes below, Q is the product of A and is released last. One representation, suggested by W. W. Cleland, follows ... 

Hie origin of tlie acceleration produced by BF in epoxide alkylation teactions has been examined tlieotetically [124], A plausible patliway for BF patLicipation in tlie epoxide-opening is sliown in Fig. 10.5. An epoxide/BF complex CPI may eti-countet tlie cuprate duster to form a ternary complex CP2, ot siidi a complex may... 

For the separation of amino acids, the applicability of this principle has been explored. For the separation of racemic phenylalanine, an amphiphilic amino acid derivative, 1-5-cholesteryl glutamate (14) has been used as a chiral co-surfactant in micelles of the nonionic surfactant Serdox NNP 10. Copper(II) ions are added for the formation of ternary complexes between phenylalanine and the amino acid cosurfactant. The basis for the separation is the difference in stability between the ternary complexes formed with d- or 1-phenylalanine, respectively. The basic principle of this process is shown in Fig. 5-17 [72]. 

The results with the [16]aneN5-Mg2+ system indicate the formation of a ternary complex according to Eq. (4). The complex formation constant is 5.6 x 104 M 1 at 25 °C... 

We have disclosed that the ligands 4c, 10, and 77, when complexed with a metal ion such as Zn2 +, Ni2+, or Co2+, become highly active toward the hydrolysis of p-nitrophenyl picolinate (7). The catalysis is most likely to occur through formation of a ternary complex in the transition state or in reactive intermediates. The metal ion in such a complex serves to activate the ligand hydroxyl group for nucleophilic attack and to orient the substrate into a favorable position to undergo the reaction. 

A classic example of where definitive experimental data necessitated refinement and extension of a model of drug-receptor interaction involved the discovery of constitutive receptor activity in GPCR systems. The state of the art model before this finding was the ternary complex model for GPCRs, a model that cannot accommodate ligand-independent (constitutive) receptor activity. 

With the experimental observation of constitutive activity for GPCRs by Costa and Herz [2], a modification was needed. Subsequently, Samama and colleagues [3] presented the extended ternary complex model to fill the void. This chapter discusses relevant mathematical models and generally offers a linkage between empirical measures of activity and molecular mechanisms. 

The resulting modification is called the extended ternary complex model [3], which describes the spontaneous formation of active state receptor ([Ra]) from an inactive state receptor ([RJ) according to an allosteric constant (L = [Ra]/[RJ). The active state receptor can form a complex with G-protein ([G]) spontaneously to form RaG, or agonist activation can induce formation of a ternary complex ARaG ... 

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