Competitive shift

In cases where the plot of [A ]/Kd vs ICS0 is not linear, other mechanisms of antagonism may be operative. If there is a nearly vertical relationship, this be due to noncompetitive antagonism in a system with no receptor reserve (see Figure 12.2d). Alternatively, if the plot is linear at low values of [A ]/Kd and then approaches an asymptotic value the antagonism may be allosteric (the value of a defines the value of the asymptote) or noncompetitive in a system with receptor reserve (competitive shift until the maximal response is depressed, Figure 12.2d). 

As stated in Sect. 4.1.1, the critical energy, E0, is reached in an appearance energy measurement only if the inequality (21) is met. The term competitive shift refers to the fact that the number of ions available for reaction to give a particular product is depleted by competing reaction channels. In eqn. (21), this possibility is represented by the exponential term. If a reaction is the lowest energy pathway of an ion, competitive shifts should not be a significant factor. 

As with kinetic shifts, the occurrence of competitive shifts is essentially an effect concerned with the sensitivity of an instrument. Given sufficient sensitivity, neither kinetic nor competitive shifts will be significant. 

Kinetic and competitive shifts are instrumental effects which, in principle, can always be avoided given sufficient sensitivity. There are other considerations germane to the determination of critical energies from appearance energies which are essential characteristics of the experimental approach. 

Energy Deposition Distributions Kinetic Shifts Competitive Shifts... 

The supply chain paradigm demands effective partnering outside the enterprise. In some ways this is easier than working only internally in some ways it s harder. It s easier because these partners are probably suppliers and customers with a common stake in your success. Clients also tell us it s sometimes easier because they can side-step internal priorities and politics. It s often harder because relationships with outsiders have traditionally been at arm s length. Whatever the case, as the basis for competition shifts to the supply chain, there will be an increase in partnering arrangements of all kinds. 

When interacting with a strongly active agonist, the multiple antagonist produces, in addition to its weak agonistic effects, a competitive shift of the curves and a non-competitive depression of the maxima, as shown in Figure 11. 

A kinetic shift can be minimized by increasing the detection sensitivity or by trapping the dissociating precursor ion and extending the time prior to mass analysis. An additional complication will arise when there is competition with another more favourable fragmentation process. This can also cause an increase in the observed AE and is often referred to as a competitive shift. 

For fragment ions other than the one of lowest appearance energy, such as AB in Figure 7.1, an additional kinetic factor, the competitive shift, also... 

---