Ternary complex formation

While high-affinity binding due to ternary complex formation (ligand binding to the receptor followed by... 

Fibrinolytics. Figure 3 Plasminogen activation (a) Kinetics of plasminogen activation by uPA (urokinase-type) and tPA (tissue-type) plasminogen activators. Effect of fibrin (b) Ternary complex formation between enzyme (tPA), substrate (Pg) and cofactor (F) Abbreviations plasmin (P), fibrin (F), plasminogen (Pg). Plasmin, formed in time, is expressed in arbitrary units. 

Hassan et al [65] used a method for the determination of primaquine and other antimalarials, through ternary complex formation. The analytical aspects of the reaction between the widely used antimalarial drugs with cobalt and thiocyanate to form ternary complexes are described. Alternatively, determination of the cobalt content of the nitrobenzene extract using atomic absorption spectroscopy provided an indirect method for the determination of the drugs. Both methods are applied to the analysis of pharmaceutical preparation and the results obtained agreed well with those obtained with official methods. 

Figure 13.1 Schematic diagram of eukaryotic translation initiation. The sites of action of small molecule inhibitors are shown with dashed lines. Kinases that affect the phosphorylation of 4E-BP and eIF2a, and exert effects on ribosome recruitment and ternary complex formation, respectively, are shown in a black box. See text for details.

A series of model siderophore molecular recognition studies coupled with host-guest carrier facilitated model membrane transport studies was reported (198-202). Three approaches were taken which incorporate (i) second coordination shell host-guest complexation, (ii) ternary complex formation, and (iii) a combination of ternary complex - second coordination shell host-guest complex formation. Examples of these approaches are described below. 

BLM transport systems for ferrioxamine B were also devised based on first coordination shell recognition via ternary complex formation utilizing vacant coordination sites on the Fe(III) center (Fig. 29) (199). The tetra-coordinated substrate complex selectively transported was partially dechelated diaqua-ferrioxamine B and coordinately unsaturated di-hydroxamato iron(III) complexes, which utilized a hydrophobic membrane bound bidentate chelator as a carrier for selective transport. Active transport for these systems was accomplished using a pH gradient (199). 

A combination first coordination shell-second coordination shell based recognition BLM transport system was devised, including active transport (200). This is based on a labile dihydroxamic acid system, including alcaligin, and a free lysine hydroxamic acid ligand capable of ternary complex formation to... 

The development of fluorescent probes for anion recognition has been very limited so far in comparison with those for cations. Most of the presently available methods of detection of anions based on fluorescence involve quenching, redox reactions, substitution reactions, ternary complex formation(15) and thus cannot be considered as recognition methods. For instance, the fluorescent sensors that are used for the determination of chloride anions in living cells are based on collisional quenching of a dye by halide ions 6-methoxy-iV-(sulfopropyl)quinoliniuni and... 

We are interested in the effect of L, compared with, on the rate constant (A-,) for the process. Ternary complex formation depicted in (4.41) has been actively studied, to a large extent because of the biological implications of the results. ... 

The classical steady-state studies of Theorell and Chance showed that the increased affinity for substrate by the NADH-bound enzyme leads to a distinct sequence of the binding of coenzyme and substrate and subsequent reaction.1442. The binding of coenzyme is a compulsory step prior to substrate binding. Release of products from the enzyme site occurs via reversal of the sequence. This mechanism, known as an ordered bi-bi mechanism because of the required order of association and dissociation of the coenzyme and substrate with ternary complex formation is summarized in Scheme 6, where E, S and P represent enzyme, substrate and product respectively. 

Dunn has also proposed a mechanism involving this charge relay system in ternary complex formation, but with the substrate displacing the zinc-bound water, as shown in Scheme 9.1443 Hydride transfer from NADH, to form an alcoholate anion, has been shown to occur before protonation.1398 As well as not requiring penta-coordinate zinc, this mechanism differs from Dworschack and Plapp s in postulating the formation of an alcoholate anion. 

In more recent years attention has turned from studying the equilibria of binary metal-amino acid complexes to that of ternary complex formation in aqueous media, particularly to complexes of the type (aa)—M11—L, where L is some other ligand or a different amino acid to (aa), and M11 is a kinetically labile metal ion. Ternary complexes involving kinetically inert metal ions, e.g. Co,w and Pt", are more well known since they can be separated from mixtures and studied in isolation. Such is not the case with the labile systems. Because of the facile nature of their equilibria they must be studied in situ (claims regarding the separation of labile species by chromatographic procedures... 

It is worth noting that in one pathway toward ternary complex formation, the equilibrium constant Aa represents the receptor affinity for ligand and Aga represents the affinity of ligand-bound receptor for G protein. In this soluble receptor system, there is an opportunity to visualize the alternate pathway directly, where Ag is the receptor affinity for G protein in the absence of ligand, and Aag is the affinity of precoupled receptor (RG) for ligand. 

The formation of these ternary luminescent lanthanide complexes was the result of displacement of the two labile metal-bound water molecules, which was necessary because the energy transfer process between the antenna and the Ln(III) metal centre is distance-dependent. This ternary complex formation was confirmed by analysis of the emission lifetimes in the presence of DMABA and showed the water molecules were displaced by a change in the hydration state q from 2 to 0, with binding constants of log fCa = 5.0. The Eu(III) complexes were not modulated in either water or buffered solutions at pH 7.4. Lifetime analysis of these complexes showed that the metal-bound water molecules had not been displaced and that the ternary complex was not formed. Of greater significance, both Tb -27 and Tb -28 could selectively detect salicylic acid while aspirin was not detected in buffered solutions at pH 7.4, using the principle as discussed for DMABA where excitation of the binding antenna resulted in a luminescent emission upon coordination of salicylic acid to the complex. 

Up to pH 2, edta (LH4) forms (TiOHL)-, and (TiOL)2 above this pH.190 Ternary complex formation in the titanium-polyphenol-aminopolycarboxylic acid system has been studied.191 Tiron forms ternary chelates with nitrilotriacetic acid, edta, and [(H02CCH2)2NCH2CH2]2NCH2C02H. Pyrocatechol, dibromogallic acid, and gallic acid form mixed complexes only with nitrilotriacetic acid. Chromotropic acid forms a complex192 with Ti,v but not with the Ti -polyphenol system. 

Gawlita E, Anderson VE, Paneth P (1995) Equilibrium isotope effect on ternary complex formation of [l-lsO]oxamate with NADH and lactate dehydrogenase. Biochemistry 34 6050-6058... 

Polyproanthocyanidin (condensed tannin) Alhagi kirgisorum (Fabaceae) PS - eIF-2 [blocks elF-Met-tRNA-GTP ternary complex formation]... 

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