Specific structure-function relations

Cubic membranes can be involved in curvature-controlled activation of certain enzymes, as well as control of enzyme activity. It is tempting to suggest the latter as a general function of cubic membranes since proteins could conceivably be located at regular points in the lattice. This could enhance transport efficiency of both product and substrate. Such mechanisms are particularly well suited for mass cooperative synthesis, such as those 

Many of the cells listed in Table 7.1 and 7.2 are involved in active membrane flow and other mass-cooperative transport phenomena. Since cubic membranes offer a high surface to-volume ratio, they may also be actively involved in these processes, perhaps as membrane storage bodies, or as transport guides. It is of interest to note that aggregates of s3maptic vesicles often resemble cubic membranes (see Chapter 5 and [136]). This can be taken as an indication of a possible on-off mechanism of membrane continuity, which might accovmt for a regulative capacity of the release of transmitter substance. 

A similar structural-functional role can be argued for in the selection of the primitive cubic membrane system in the bioluminescent scaleworms, whose structure is apparently also invariant. 

As seen in Table 7.1 and 7.2, there are, in addition to these two examples, several other photoactive cells in which we have identified cubic membranes. In the case of the mitochondrial cubic membrane in Tupaia gUs we can speculate that the use of an isotropic structure allows efficient capture of the incoming light, which has to pass the giant mitochondria before reaching the outer segment. Similar reasons may guide the choice of a cubic membrane system in the lens of certain scaleworms. 

The hyperbolic architecture of a variety of enzymes has been pointed out in Chapter 6. It seems natural then that enzymes encapsulated in a hyperbolic (lipid) environment (of suitable dimensions) are able to adopt their favoured architecture, and thus perform their biochemical task efficiently. In this context, it is wortii noting that remarkable increases in enzymatic efficiency of biochemical s3mthesis have been achieved by containment of enzymes in cubosomes, rather than conventional (flat) liposomes. 

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There are many ligands and group-specific reagents that have been demonstrated to alter the properties of H,K-ATPase, and which are not clinically useful. For example, there is a variety of chemicals that have been used in studies on structure-function relations of H,K-ATPase and that inhibit the enzyme in vitro by modification of its amino [49,67,158], sulfhydryl [95,165,166] or carboxyl groups [140]. 

The absence of a high-resolution structure of any transporter in the NT family greatly complicates the interpretation of structure-function studies. The recent identification of the bacterial and archaeal transporters and their potential suitability for direct structural studies raises the exciting prospect of being able to test specific structural hypotheses related to transport. In the meantime, the use of the numbering scheme introduced here in a context of predicted structural properties should facilitate communication among researchers on different members of the transporter family as the mechanistic details are being probed. 

In the last few years, kinetic studies with proteinase mutants taught us much more about the complexity and intricacy of structure-function relations of proteinases. They focused, in many cases, on the effects of single residues on k and Such details of the mechanism encourage theoreticians to construct sophisticated models that are able to answer specific questions and to report energies that may be compared to experiments. 

Abstract Shape-memory polymers (SMPs) are able to fix a temporary deformed shape and recover their original permanent shape upon application of an external stimulus such as heat or light. A shape-memory functionalization can be realized for polymer based materials with an appropriate morphology by application of a specific shape-memory creation procedure (SMCP). Specific characterization methods have been tailored to explore the structure-function relations of SMPs in respective applications. This paper reviews characterization methods on different length scales from the molecular to the macroscopic level. 

The much simplified picture of the energetics and kinetics for a working DSSC device, which emerged in the early research,is still useful as an introduction of working principles. The chemical complexity of the device must, however, be understood and mastered to improve our ability to identify predictive materials and optimised structure/function relation-ships. The present understanding of these processes is now covered with specific emphasis on the electron transport through the mesoporous TiOi electrode. The reader is also directed to recent review articles on these topics. 

Nonrepetitive but well-defined structures of this type form many important features of enzyme active sites. In some cases, a particular arrangement of coil structure providing a specific type of functional site recurs in several functionally related proteins. The peptide loop that binds iron-sulfur clusters in both ferredoxin and high potential iron protein is one example. Another is the central loop portion of the E—F hand structure that binds a calcium ion in several calcium-binding proteins, including calmodulin, carp parvalbumin, troponin C, and the intestinal calcium-binding protein. This loop, shown in Figure 6.26, connects two short a-helices. The calcium ion nestles into the pocket formed by this structure. 

Among chiral auxiliaries, l,3-oxazolidine-2-thiones (OZTs) have attracted important interest thanks to there various applications in different synthetic transformations. These simple structures, directly related to the well-documented Evans oxazolidinones, have been explored in asymmetric Diels-Alder reactions and asymmetric alkylations (7V-enoyl derivatives), but mainly in condensation of their 7V-acyl derivatives on aldehydes. Those have shown interesting characteristics in anti-selective aldol reactions or combined asymmetric addition. Normally, the use of chiral auxiliaries which can accomplish chirality transfer with a predictable stereochemistry on new generated stereogenic centers, are indispensable in asymmetric synthesis. The use of OZTs as chiral copula has proven efficient and especially useful for a large number of stereoselective reactions. In addition, OZT heterocycles are helpful synthons that can be specifically functionalized. 

Eppler et al. [103] viewed these results as having a potential relationship to salt-activated enzyme preparations, particularly in relation to the mobility of enzyme-bound water. Specifically, the authors examined both water mobility [as measured by T2-derived correlation times, (tc)D20] and NaF-activated enzyme activity and observed a linear relationship. This suggests that the salt-activated enzymes contain a more mobile water population than salt-free enzymes, which facilitates a more aqueous-like local environment and dramatically increases enzyme activity through increased flexibility. Therefore, enzyme activation appears to correlate with the properties of enzyme-associated water. Once again, the physicochemical properties of water dictate enzyme structure, function, and dynamics. Hence, salt activation has proven to be a useful technique in activating enzymes for use in organic solvents and has provided a quantitative tool to better understand the role of water in enzymatic catalysis in dehydrated media. 

The issue of drug selectivity is related closely to the fact that many receptor populations can be divided into various subtypes according to specific structural and functional differences between subgroups of the receptor. A primary example is the cholinergic (acetylcholine) receptor found on various tissues throughout the body. These receptors can be classified into two primary subtypes muscarinic and nicotinic. Acetylcholine will bind to either subtype, but drugs such as nicotine will bind preferentially to the nicotinic subtype, and muscarine (a toxin found in certain mushrooms) will bind preferentially to the muscarinic subtype. 

Mechanistic studies of RNA enzymes (ribozymes) and ribonucleoprotein (RNP) complexes such as the ribosome and telomerase, often seek to characterize RNA structural features, either dynamic or static, and relate these properties to specific catalytic functions. Many experimental techniques that probe RNA structure-function relationships rely upon site-specific incorporation of chemically modified ribonucleotides into the RNA of interest, often in the form of chemical cross-linkers to probe for sites of protein-RNA interaction or small organic fluorophores to measure dynamic structural properties of RNAs. The ability to arbitrarily modify any RNA molecule has been greatly enabled by modern RNA synthesis techniques however, there remains a practical size... 

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