Transport Kinetic Constants

Pflra-chloromercunphenylsulfonate is the most potent glycine uptake inhibitor known to date, but imipramine, chlorpromazine, and hydrazinoacetic acid all have some inhibitory action (Aprison et al., 1970). 

The uptake of taurine in glial cells and neurons is strongly inhibited in the presence of p-alanine GABA and hypotaurme are strong inhibitors of taurine uptake in brain slices (Lahdesmaki and Oja, 1973). In cultured glioma cells, GABA and taurine are competitive inhibitors of each other s uptake, and this may indicate a common transport system 

For estimating the initial rate of uptake of amino acids into cellular material, a detailed experimental protocol was selected from Shank and Campbell (1984) and is given below. Various other procedures that differ in detail, but contain the same concept, are to be found in the literature for example, Iversen and Neal (1968). 

In these experiments, 50 fxL samples of cellular material containing the equivalent of 5-30 xg of protein are added to 150 xL of an incubation medium containing 0.02-0.05 )j,Ci of a C-labeled 

Release of an ammo acid may be studied by loading the preparation with radiolabeled, exogenous amino acids. Then the preparation is continuously superfused and the radioactivity in the collecting fluid is monitored. Alternatively, endogenous, nonlabeled amino acids released by the preparation can be determined in the superfusate. 

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This gives the following transport kinetic constants ... 

Figure 13 Mediated transport kinetic scheme. C = carrier, S = solute 1 and 2 represent sides of the membrane g are rate constants for changes in conformation of solute-loaded carrier k are rate constants for conformational changes of unloaded carrier f and bt are rate constants for formation and separation of carrier-solute complex. (From Ref. 73.)...

The kinetic constant, ki can be calculated from Lewis cell experiments [46] under the condition of higher carrier concentration compared to that of solute in aqueous phase, so that the mass transfer rate is controlled by the transport of the solute to the interface and the rate of reaction at the interface. 

The model active transport system described by Dr. Thomas is based on an asymmetric arrangement of two enzymes. A model active transport system was also described by Blumenthal et al. several years ago based on a single enzyme immobilized between asymmetric boundaries [Blumenthal, Caplan, and Kedem, Biophys. J., 7, 735 (1967)]. In the latter case the phenomenological coefficients were measured, and it was possible to demonstrate Onsager symmetry and the correlation between the thermodynamic coefficients and the kinetic constants. 

The chemical kinetics approach provides us with more insight with respect to the range of validity. We see from Table 4 that Fick s law indeed results without approximations (l.h.s.). For the pure electrical conduction (r.h.s.) we have to linearize the exponentials (Eqs. 98 and 99), i.e., to assume Ifa I RT which is definitely a good approximation for transport in usual samples it fails at boundaries or for ultrathin samples. Hence the application of Eq. (103) has to presuppose sufficiently thick samples and not too high fields. Table 4 also reveals the connection between Dk, uk and the transport rate constant kk and hence their microscopic meaning ... 

At this juncture, it is presumed that the regeneration order and kinetic constant or in general, the regeneration behavior changes due to significant transport resistance or oxygen accessibility limitation. 

Finally, this study provides an extensive set of data on thick wood pyrolysis which can be better interpreted and generalized by the use of mathematical models taking into account the effects of transport phenomena and chemical reactions. Models including such features are already available in the literature (for instance, see References 23,24) and have proven to give quantitative predictions of temperature dynamics, but product yield predictions are still unacceptable, mainly because of unreliable kinetic constants. Therefore, this issue deserves further investigation before extensive computer simulation and/or development of more advanced physical models of thick wood pyrolysis are proposed. 

General Motors Research and Development Center is developing a Pt/Al203 600 cell/in. 2 cordierite monolith reactors to remove the CO concentration in a full cell feed stream. They have developed a reactor model to better understand the interaction between kinetic control and transport limitations during the Prox reactions. Two combined groups of kinetic constants are derived that characterize the rates. The resulting experimentally measured net conversion rates are fit to the model rate expressions.62,63... 

Peak photocurrents excited In a polymer of bis ( -toluene-sulfonate) of 2,4-hexadlyne-l,6-dlol (PTS) by N2-laser pulses vary superquadratically with electric field. The ratio ip(E)/((i(E), where ()i denotes the carrier generation efficiency, increases linearly with field. This indicates that on a 10 ns scale the carrier drift velocity is a linear function of E. Information on carrier transport kinetics in the time domain of barrier controlled motion is inferred from the rise time of photocurrents excited by rectangular pulses of A88 nm light. The intensity dependence of the rate constant for carrier relaxation indicates efficient interaction between barrier-localized carriers and chain excitons promoting barrier crossing. 

Mass transport Rate constants Reaction kinetics Sensor Sirnface plasmon resonance... 

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