Gated rate constant

At a different membrane potential the gating rate constants would differ. 

R is the distance between the molecular centers of TIM and GAP at contact]. For such a rapidly gated, diffusion-controlled reaction, the gated rate constant k is simply given by the rate constant for the enzyme with the gate held open,i°2 and, to the substrate, the gates appear to be open all the time. Thus,... 

Figure 2. Kinetic schemes for Na channel gating (right) and the graphed time-course for single channels (solid lines, the higher position is open ) and for the population of many channels (broken line, the fraction open increases upwardly). Numbers at the arrows of the kinetic scheme are the rate constants, in 10 sec" The period of simulation is 5 msec. Computerized model courtesy of Dr. Daniel Chemoff.

If M is unstable then ipb/fpf will be less than unity. Its magnitude will depend upon the scan rate, the value of the first-order constant k, and the conditions of the experiment. At fast scan rates the ratio ipb/ ip, may approach one if the time gate for the decomposition of M is small compared with the half-life of M-, (In 2jk). As the temperature is lowered, the magnitude of k may be sufficiently decreased for full reversible behaviour to be observed. The decomposition of M- could involve the attack of a solution species upon it, e.g. an electrophile. In such cases, ipb/ipf, will of course be dependent upon the concentration of the particular substrate (under pseudo-first-order conditions, k is kapparent). Quantitative cyclic voltammetric and related techniques allow the evaluation of the rate constants for such electrochemical—chemical, EC, processes. At the limit, the electron-transfer process is completely irreversible if k is sufficiently large with respect to the rate of heterogeneous electron transfer the electrochemical and chemical steps are concerted on the time-scale of the cyclic voltammetric experiment.1-3... 

In order to determine the rate equation for hydrodesulfurization, a semi-logarithmic plot of the total sulfur content with time was made (Figure 2). The plot indicated two independent first-order reactions with greatly different rate constants. This is in agreement with the findings of Gates, et al. (7) and Pitts (3). A procedure similar to that of Pitts (3 ) was used to describe the hydrodesulfurization kinetics. The rate expression is given below ... 

The kinetic data and the information about linkage isomerization and redox potentials demonstrated that electron transfer takes place by path A, where [Ru(NH3)5(n-buso)]2+ is first oxidized by cis-[Ru(NH3)4(pyridine 4-carboxya-mide)2]3+ against a 24 kj mol-1 up-hill electron transfer with the rate constant over 50 M-1 s-1 and, in the second step, the Ru3+SO isomerizes to Ru3+OS with a rate constant of 4.3 s-1. This conclusion is interesting to consider as the mechanism not only for biological but also for the gated electron transfer systems. 

Akk et al. (92) constructed the homologous mouse mutation eD175N to test the effects on the rate constants of binding and gating. By use of high concentrations of ACh and Popen curves, the ECgo value of eD175N was found to... 

---