Speculative models

The intramembranous domain of Ca -ATPase contains of the mass of the ATPase molecule based on electron microscopy of Ca -ATPase crystals [90,91] and X-ray diffraction analysis of oriented multilayers of sarcoplasmic reticulum [140]. Although in speculative models developed from these reconstructed structures the intramembranous domain was pictured as containing ten transmembrane helices [141,142], at the resolution attainable so far, several alternative transmembrane arrangements would be equally possible. 

Fig. 5. A speculative model for the arrangement of the helical regions of the sugar transporters in the membrane. The helices are numbered as shown in Fig. 4. The small circle labelled s represents a glucose molecule.

The Defective Nature of TS-1 Material Speculative Model of Framework Sites... 

Although the above discussion seems reasonable, its difficult either to take it much further or even to ascertain the likelihood of the scenarios presented without more detailed three-dimensional calculations on the nonadi-abatic crossing region between the B lf2 and R surfaces.4,32,36-39 It should be stressed that the scenarios are not presented as an exact mechanism but rather as a speculative model which qualitatively explains the trends in our data. 

Schemes Speculative model for nanopattern formation from tethered Si/Si02//PS-l)-PMMA...

Before plunging into a discussion of how such complexes are prepared, it is perhaps worthwhile to consider explicitly the rationale for such activity. The synthesis and characterization of accurate model complexes for a given metal site in a protein or other macromolecule allows one to (l) determine the intrinsic properties of the metal site in the absence of perturbations provided by the protein environment or (il) in favorable cases, deduce the structure of the metal site by comparison of corresponding physical and spectroscopic properties of the model and metalloprotein (3). The first class of model complexes has been termed "corroborative models" by Hill (4), while the second are termed "speculative models" (4). To date, virtually all the major achievements of the synthetic model approach have been in development of corroborative models. 

Figure 2. A speculative model for the assembly and growth of the Dicotyledonous cell wall. For clarity, the model shows two microfibrils ===, ===)...

Post RM, Weiss SRB A speculative model of affective illness cyclicity based on patterns of drug tolerance observed in amygdala-kindled seizures. Mol Neurobiol... 

D. A Speculative Model of Hydrocarbon Reactions on Metals and Alloys... 

The discriminative uptake of alkali metal cations by biological systems, through their membranes, has been an area of much interest. In the membrane, the cations must pass through a lipid bilayer of low dielectric constant and this has led to the proposition that the cation could be selectively transferred via a carrier molecule, or through a suitably donor-lined pore.7-9 As a consequence of their selective properties, the polyethers and cryptands have been investigated as speculative models for the above process and selectivity sequences have been established. 

The goal of our research over the past few years has been to understand better the molecular events involved in systemic acquired resistance. Our current hypothesis of the phenomenon is detailed in Fig. 7. This is a speculative model at this stage but it serves as our working hypothesis on which to plan future experiments. When pathogen infection induces a necrotic lesion many biochemical changes take place. Among these are... 

In response to this data, work by David Fenton of the University of Sheffield, UK,6 resulted in the bimetallic Cu(II) Schiff s base species 12.19. This coordination complex, which is a speculative model, exhibits many of the expected features of the natural enzyme, such as a Cu---Cu separation of 3.64 A, endogeneous alkoxo bridge and small antiferromagnetic coupling, Figure 12.6. 

There are two basic kinds of chemical models structural and functional. Functional models are harder to design and may not physically resemble the system they are designed to mimic (e.g. hydraphiles) but do make use of the same concepts. Was can also distinguish confirmatory and speculative models depending on whether the model is based on a known biological structure or not. 

Enzymological and redox potentiometric studies by EPR have indicated that the catalytic sites of the oxygen-stable [Ni-Fe] hydrogenases exhibit at least six enzy-mologically distinct states [75-78], These are schematically represented in Figure 3, which depicts a speculative model for the hydrogenase redox cycle, as discussed later. 

Figure 3 Speculative model for the hydrogenase enzyme cycle such as that from D. gigas. The highest oxidation states of the enzyme are at the top, and each step down corresponds to a one-electron reduction. Some hydrons that are transferred to sites in the protein are not shown. Redox states of the iron-sulfur clusters are omitted.

Abstract. Muonium is a hydrogen-like system which in many respects may be viewed as an ideal atom. Due to the close confinement of the bound state of the two pointlike leptons it can serve as a test object for Quantum Electrodynamics. The nature of the muon as a heavy copy of the electron can be verified. Furthermore, searches for additional, yet unknown interactions between leptons can be carried out. Recently completed experimental projects cover the ground state hyperfine structure, the ls-2s energy interval, a search for spontaneous conversion of muonium into antimuonium and a test of CPT and Lorentz invariance. Precision experiments allow the extraction of accurate values for the electromagnetic fine structure constant, the muon magnetic moment and the muon mass. Most stringent limits on speculative models beyond the standard theory have been set. 

Beyond atomic spectroscopy muonium renders the possibility to search directly and sensitively for yet unknown interactions between the two charged leptons from two different generations. Among the mysteries observed for leptons are the apparently conserved lepton numbers. As a matter of fact, several distinctively different lepton number conservation schemes appear to hold, some of which are additive and some are multiplicative, parity-like. Some of them distinguish between lepton families and others don t [46,47,48,49,50]. No local gauge invariance has been revealed yet which would be associated with any of these empirically established laws. Since there is common believe [51] that any discrete conserved quantity is connected to a local gauge invariance, a breakdown of lepton number conservation is widely expected, particularly in the framework of many speculative models. 

This new result, which exceeds bounds from previous experiments [58,64] by a factor of 2500 and the one from an early stage of the experiment [59] by 35, has some impact on speculative models. A certain model is ruled out with more than 4 generations of particles where masses could be generated radiatively with heavy lepton seeding [66]. A new lower limit of... 

Figure 13 Speculative model for the diferrous site in XyM (Ref. 87, 2003 Springer Verlag)...

As understanding of a particular metalloprotein develops, so the questions to be addressed by models change and last year s model can become dated very rapidly. To use the terms introduced by Hill (5) and expanded by Fenton (6), the normal progression is from speculative models through corroborative ones to fully functional S3mthetic analogs. The aims of this process are twofold, to understand the structure... 

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