Sequential model

The automotive sector s quality assurance standard QS 9000 (1998) suggests a concurrent high level model, as opposed to the sequential model from BS 7000 (1997). This is shown in Figure 5.7. The automotive industry in particular has embraced the use of concurrent engineering models for product development, and this is reflected in the standards which facilitate their quality assurance programmes. A concurrent industrial model from the automotive sector will be discussed later. 

This concerted model assumes furthermore that the symmetry of the molecule is conserved so that the activity of all its subunits is either equally low or equally high, that is, all structural changes are concerted. Subsequently Daniel Koshland, University of California, Berkeley, postulated a sequential model in which each subunit is allowed independently to change its tertiary structure on substrate binding. In this model tertiary structural changes in the subunit with bound ligand alter the interactions of this... 

FIGURE 2.9. Sequential Model of Error Causation Chain (based on Rasmussen, 1982). 

APPENDIX 2B FLOWCHARTS FOR USING THE RASMUSSEN SEQUENTIAL MODEL FOR INCIDENT ANALYSIS (Petersen, 1985)... 

APPENDIX 2C CASE STUDY ILLUSTRATING THE USE OF THE SEQUENTIAL MODEL OF ERROR IN INCIDENT ANALYSIS... 

Further links exist between the PIF concept and topics considered in previous chapters. In Chapter 2 the sequential model developed by Rasmussen to represent the error process from its initiator to its consequences was described (Figure 2.9). In this process, the PIFs were shown as being involved in both the initiating event and the internal error mechanisms. In the application example of the model in Appendix 2C, the PIF which constituted the initiating event was the distracting environment, and poor ergonomics of the panel was a PIF which influenced the internal error mechanism. 

COMPLEX I is a multiple point-source code with terrain adjustment representing a sequential modeling bridge between VALLEY and COMPLEX II. 

The effect of structural modification to 22 on the binding efficiency and binding dynamics of hairpin DNA immobilized on metal surfaces were studied using surface plasmon resonance.124,125 The association and dissociation kinetics were analyzed using a sequential model for the binding of the imidazole containing polyamides... 

The sequential model developed by Koshland and Nemethy (1966) (Figure 3.3b). 

The quantum results (thick lines) of the sequential model (a) are seen to completely decay in the diabatic electronic ground state of the system. For short times, furthermore, the model predicts transient electronic population in the intermediate state. In the superexchange model (b), on the other hand, there is a nonvanishing long-time population of the initial diabatic state, whereas the intermediate state is hardly ever populated. We have performed classical mapping simulations with ZPE correction (a) y = 0.6 and (b) y = 0.34. The ZPE corrections have been calculated via Eq. (98) and are only employed to the... 

The second extreme case, suggested by Koshland, Nemethy, and Filmer (KNF) (Koshland et al., 1966), is also known as the sequential model. The mathematical conditions required to obtain this limiting case are quite severe. First, it is assumed that, in the absence of a ligand, one of the conformations is dominant, say the LL form. In addition, it is assumed that a ligand binding to any subunit will change the conformation of that subunit into the H form. These assumptions lead to the consideration of only the four diagonal states of Fig. 4.18, for which the PF is... 

The empty state is the LL state on the top left comer of Fig. 4.18. The binding of a ligand on any of the subunits will shift its conformation completely from L to H without affecting the conformation of the second subunit. Binding of the two ligands will shift the entire polymer to the state HH. Thus, in each binding process there is a total change of conformation of one subunit hence the term sequential model. 

We have interpreted the principal denaturation peaks in our data in terms of multiple sequential transitions, but in fact most of the peaks in the data base can be fitted almost as well by a model involving two independent transitions. For endotherm envelopes of this size and degree of asymmetry, the differences between the fits obtained from sequential and independent models are too small to allow a choice of one or the other based simply on goodness of fit. Our provisional preference for the sequential model is based on other considerations, one being the failure of a 3.5-unit... 

Selected entries from Methods in Enzymology [vol, page(s)] Activation, 64, 177 concerted allosteric model, 64, 173 isotope exchange properties, 64, 10 negative cooperativity, 64, 189 rapid relaxation measurement, 64, 188, 189 sequential model, 64,... 

A model used to explain cooperativity on the basis of ligand-induced changes in conformation that may or may not alter the subunit-subunit interfaces of oligomeric enzymes and receptors. This model has also been referred to as the Adair-Koshland-Nemethy-Filmer model (AKNF model), the induced-fit model, and the sequential model. 

Two major models are typically used to describe these situations the concerted model and the sequential model. In the concerted model, the enzyme has two major conformations a relaxed form that can bind the appropriate reactant molecule(s) and a tight form that is unable to tightly bind the reactant molecule(s). In this model, all subunits containing reactive sites change at the same time (Figure 16.7). An equilibrium exists between the active and inactive structures. Binding at one of the sites shifts the equilibrium to favor the active relaxed form. 

In the second model, the sequential model (Fig. 5-15b), proposed in 1966 by Daniel Koshland and colleagues, ligand binding can induce a change of conformation in an individual subunit. A conformational change in one subunit makes a similar change in an... 

Two major models have been proposed to explain the cooperative binding of ligands to multisubunit proteins the concerted model and the sequential model. 

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). 

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