Carrier, model

By structural complementarity, dicationic l,4-diazabicyclo[2.2.2]octane (VII) provides an appropriate recognition site for phosphate ions and two stearyl side chains attached to the amines add lipophilic properties 59,60). Such a carrier model can selectively extract nucleotides from aqueous solution to chloroform solution via lipophilic salt formation. The order of nucleotide affinity is ATP > ADP > AMP. The selectivity ratios were 45 for ADP/AMP and 7500 for ATP/AMP at pH 3. The relative transport rate was ATP > ADP > AMP. The ratios were 60 for ATP/AMP and 51 for ADP/AMP. The modes of interaction of ADP and ATP are proposed to be as shown in Fig. 6. 

All the results were obtained from estimates of initial rates made using fresh blood. The predicted values for Km and VmnK (shown in parentheses) are taken from Wheeler and Whelan [65] who fitted the data to the asymmetric carrier model by the procedures described in Wheeler [52],... 

Fig. 2. The simple asymmetric carrier model for glucose transport. C denotes a sugar-binding site, which can exist in an outward-facing (Co) or an inward-facing (Ci) conformation. Dissociation constants for sugar binding are bja and ejf. Rate constants for carrier re-orientation are c, d, g, and h.

These relationships are identical to Haldane relationships, but unlike the latter, their validity does not derive from a proposed reaction scheme, but merely from the observed hyperbolic dependence of transport rates upon substrate concentration. Krupka showed that these relationships were not obeyed by the set of data previously used by Lieb [64] to reject the simple asymmetric carrier model for glucose transport. Such data therefore cannot be used either to confirm or refute the model. 

Assuming that the simple, four-state asymmetric carrier model does accurately describe the transport process, Lowe and Walmsley [48] have exploited the tempera-... 

Because the rates of sugar binding to and dissociation from the transporter are very rapid compared to the rates of transporter re-orientation, the Michaelis constants for transport by the simple asymmetric carrier model are given by the following equations,... 

The evaluation of kinetic properties of NRPS systems is a problem of generally underestimated complexity. The basic path was established in 1971, defining activation, thiolation, and peptidyl transfers as basic reactions. The further refinement from structural data to establish the multiple carrier model, and now to tackle domain interactions, has added some precision to the questions asked. However, we have not yet arrived at a complete kinetic description of even the simple tripeptide synthetase. The ACV synthetase operates with four different substrates at six binding sites, releasing 3 moles of AMP and 3 moles of MgPPi for each ACV formed at optimal conditions [51], A sequence of 10 reactions has been... 

T Stein, J Vater, V Kruft, A Otto, B Wittmann-Liebold, P Franke, M Panico, R McDowell, HR Morris. The multiple carrier model of nonribosomal peptide biosynthesis at modular multienzymatic templates. J Biol Chem 271 15428-15435,1996. 

FIGURE 3.11 Schematic illustration of the cross section of different carrier models gimbal type (A), floating type (B and C), and actual example of a carrier (D). 

Faas, H. et al., Monitoring the intragastric distribution of a colloidal drug carrier model by magnetic resonance imaging, Pharm. Res., 18(4), 460, 2001. 

The high temperature experiments [19, 27, 90—94] were performed with all the inert gases as diluents, and a set of precise data has been compared [27] with several theories [95—100] dealing with the collision partner effect. The experimental results showed little variation with regard to the identity of the inert gas and corresponded most closely to the predictions of the Keck—Carrier model [100]. The efficiencies were expressed on a per collision basis, fe,/Z (Kr as reference), at 1500°K He (0.354), Ne (0.830), Ar (0.869), Kr (1.00), Xe (0.870). The efficiency of CO2 in promoting bromine dissociation [101] has been determined to be... 

Following the pioneering work of the Dundee group (LeComber and Spear, 1970 LeComber et ai, 1977 Jones et ai, 1977 Allan et ai, 1977) several researchers (Jan et ai, 1979, 1980 Anderson and Paul, 1982) have interpreted their transport data in terms of a two-carrier model At higher temperatures, transport is by extended states, whereas at lower temperatures NNH in tail states or donor states is pedominant. The transport formulas... 

Fig. 3. Calculated curves of G as a function of 1/rfor two-carrier model using parameters of (a) Jones et al. (1977) and (b) Anderson and Paul (1982). Curve numbers indicate sample numbers in references.

The analysis of the spectral dependence of /p in the presence of surface recombination should yield the minority-carrier diffusion length Lp and S, the ratio of the surface recombination velocity to the bulk diffusion velocity. DeVore (1956) presented an analysis using a single carrier model in which local charge neutrality is maintained by fast dielectric relaxation. Schetzina... 

Fig. 4. The principal reactions of the carrier model. M denotes a metal ion. S denotes the uncomplexed carrier. MS devotes the complex. The reactions in the top line are heterogeneous An ion in the aqueous phase joins or leaves a carrier in the membrane phase. The reactions in the lower line are homogeneous Complexation or dissociation takes place between a carrier and an ion in the same phase. (Ions cannot exist in the membrane phase because of high Born charging energy.)...

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