Sequential interaction model generalized

From the binding sequences in reaction (13.79), we can see that the general KNF model takes into account a variety of possible subunit interactions that are able to affect affinities of vacant sites. Therefore, the general KNF model is far more versatile than the simple sequential interaction model or, for that matter, than the MWC model. 

The simple sequential interaction model is more general than the concerted-symmetry model in that there are many combinations of values for a, b, and c, for which there are no equivalent values of L and c. Furthermore, the... 

The MWC concerted-symmetry and KNF sequential interaction models may be considered as extreme cases of the more general model shown in Fig. 19. A general model for a four-site allosteric enzyme involves the hybrid oligomers. The first and the fourth column in Fig. 19 represent the concerted-symmetry model. The diagonal represents the sequential interaction model. As shown, there are 25 different types of enzyme forms. If the potential nonequivalent complexes are included (such as, e.g., two different T3RS2), the number raises to 44 possible enzyme forms (Hammes Wu, 1971). 

Sigmoid kinetic behavior generally reflects cooperative interactions between protein subunits. In other words, changes in the structure of one subunit are translated into structural changes in adjacent subunits, an effect mediated by noncovalent interactions at the interface between subunits. The principles are particularly well illustrated by a nonenzyme 02 binding to hemoglobin. Sigmoid kinetic behavior is explained by the concerted and sequential models for subunit interactions (see Fig. 5-15). 

The theoretical approaches aimed at a description of nonlinear adsorption regimes are discussed next—in particular the elassieal, random sequential adsorption (RSA) model. The role of polydispersity, particle shape, orientation, and electrostatic interactions is elucidated. Then, the generalized RSA model is presented, which reflects the coupling of the surface transport with the bulk transfer step governed by external force or diffusion. 

We developed a general model which includes contributions from both CIDEP and CRPP. In this paper, we apply this model to sequential electron transfer in photosynthetic bacteria. Our model calculates the density matrix for the P r radical pair and transfers the polarization as it develops to the P Q radical pair. We illustrate several possible cases. One case is equivalent to CIDEP no interactions are included on the secondary radical pair, P Q. Another approximates CRPP by either increasing the transfer rate from P r to P Q" or restricting interactions to the secondary radical pair, P Q. Others allow interactions on both the primary and secondary radical pairs with various transfer rates. 

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