Species-specific affinity

In Chap. 2 we analyzed single variable linear and non-linear systems with single and multiple stable stationary states by use of the deterministic equations of chemical kinetics. We introduced species-specific affinities and the concept of an excess work with these we showed the existence of a thermodynamic state function 4> and compiled its many interesting properties, see (2.15 2.19), including its relation to fluctuations as given by the stationary solution of the master equation, (2.34). We continue this approach here by turning to systems with more than one intermediate, [1]. 

We identify species-specific affinities for X and T, — fix) and (py — Py), both of which vanish at the stationary state. They are related to the reaction rates by the equations... 

We can find an interpretation of the species-specific affinities with a thought experiment carried out in the apparatus shown in Fig. 4.1. 

Hence we see that the species-specific affinity is an excess free energy, an excess work,... 

We need again the concept of thermodynamic and kinetic indistinguisha-bility of the given non-linear system with a specified linear system the state variables, equilibrium constants, and quantities derivable from them are identical and so are the kinetic terms. The species-specific affinities, marked by a star, must satisfy two conditions (nx — Mjf) My) must each vanish... 

We have defined a thermodynamic state function for the linear system in (2.6, 2.5), and for the nonlinear system in (2.13, 2.12), in each case in terms of species-specific affinities and the kinetic rates in the forward and reverse reactions. (We labeled these state functions there with (j) and cj), respectively, but use here the common label cf)). With two definitions, one for the net rate of the reaction... 

What are the advantages of the formulation, (18.8) The term t x) is the net flux of the deterministic kinetics, (18.6), and the derivative of the state function (j> is the species specific affinity, (/tx — for the linear case, or (/Xx — /x x) for the nonlinear case, the driving force for the reaction toward a stationary state. Thus we have a flux-driving force relation. Second, the formulation is symmetric with respect to /+(x) and t (x), which is not the case with other formulations. Third, the state function 4> determines the probability distribution of fluctuations in x from its value at the stationary state, see (2.34). Further, as we shall show shortly, the term D x) is a measure of the strength... 

Here the species-specific affinity is small and tanhy y and (18.8) reduces to... 

In humans as well as in other but not all mammalian species, kininogens are modified by posttranslational hydroxylation of a single proline residue of their kinin sequence, i.e. position 3 in bradykinin or position 4 in kallidin. Hydroxylation appears not to affect the specificity, affinity or intrinsic efficacy of the kinins. 

Biological activity can be evaluated by using in vitro techniques to determine which effects of the product are related to clinical activity. Due to species specificity of biotechnology derived products, it is necessary to select relevant species for testing. Mammalian cell lines can be used to predict in vivo activity and the relative sensitivity of various species including man. Such studies are useful to determine receptor occupancy, receptor affinity pharmacological aspects, and for the selection of adequate animal species for toxicity testing. 

Monoclonal immunoreagents offer advantages of uniformity, specificity, constant affinity, and availability in virtually unlimited supply, compared with their polyclonal counterparts. Species-specific immunoreagents, such as HSA-1, will allow the archaeological and forensic communities to standardize the identification of human blood and tissue and the direct comparison of results from different laboratories without doubt about the specificity of the antibody. 

The driving force for this charge formation is again of a non-electrostatlc, or chemical nature, as defined In sec. 3.2. and requires preferential enrichment of one of the ionic species. Such a preference is not caused by specific affinity toward the vapour phase, but by a lower reluctance to leave the bulk, l.e. to become dehydrated. Most simple electroljdes have strongly hydrated Ions, which avoid the surface so that they are negatively adsorbed. 

Wilks SA, Keevil CW. Targeting species-specific low-affinity... 

---