Changes in Conformation

Even in the absence of flow, a polymer molecule in solution is in a state of continual motion set forth by the thermal energy of the system. Rotation around any single bond of the backbone in a flexible polymer chain will induce a change in conformation. For a polyethylene molecule having (n + 1) methylene groups connected by n C — C links, the total number of available conformations increases as 3°. With the number n encompassing the range of 105 and beyond, the number of accessible conformations becomes enormous and the shape of the polymers can only be usefully described statistically. 

The same inversion occurs in the case of the trans isomer10. Changes in conformational properties when passing from the neutral to the corresponding radical anion is a recent and well-documented topic in conformational analysis17-21. 

An example of this effect, called conformational transmission, is found in ergost-7-en-3-one (5) and cholest-6-en-3-one (6), where 6 condenses with benzaldehyde 15 times faster than 5. The reaction site in both cases is the earbonyl group, and the rate increases because moving the double bond from the 7 to the 6 position causes a change in conformation at the carbonyl group (the difference in the side chain at C-17 does not affect the rate). 

For many solubilized enzymes the greatest catalytic activity and/or changes in conformation are found at R < 12, namely, when the competition for the water in the system between surfactant head groups and biopolymers is strong. This emphasizes the importance of the hydration water surrounding the biopolymer on its reactivity and conformation [13], It has been reported that enzymes incorporated in the aqueous polar core of the reversed micelles are protected against denaturation and that the distribution of some proteins, such as chymotrypsine, ribonuclease, and cytochrome c, is well described by a Poisson distribution. The protein state and reactivity were found markedly different from those observed in bulk aqueous solution [178,179],... 

The CD spectrum of the C188S mutant is essentially the same as that of the wild-type enzyme, which reflects that the tertiary structure of this mutant changed little compared to that of the wild-type enzyme. Calculation of the content of secondary structure of the mutant enzyme based on J-600S Secondary Structure Estimation system (JASCO) also showed that there is no significant change in the secondary structure of the mutant. The fact that the k value of this mutant is extremely small despite little change in conformation clearly indicates that Cysl88 is located in the active site. 

In some situations, the direct attachment of a large group (such as fluorescamine) to a biologically active substrate can reduce activity. This is due to steric hindrance which can cause a change in conformation or physically block an active site. This condition can be obviated in many cases by attaching the bulky moiety to a spacer arm composed of two or more methylene groups. To this end, a variant of F-D was also synthesized in which a spacer arm of beta-alanine was inserted between the fluorescent and chemically reactive moieties of the reagent. 

Figure 13 Mediated transport kinetic scheme. C = carrier, S = solute 1 and 2 represent sides of the membrane g are rate constants for changes in conformation of solute-loaded carrier k are rate constants for conformational changes of unloaded carrier f and bt are rate constants for formation and separation of carrier-solute complex. (From Ref. 73.)...

Harkness, P., Millar, N. Changes in conformation and subcellular distribution of a4b2 nicotinic acetylcholine receptors revealed by chronic nicotine treatment and expression of subunit chimeras. J. Neurosci. 22 10172, 2002. 

On the model of the receptors in the bioinformation networks, several types of molecular assemblies may be designed for molecular information transduction. The molecular assembly should contain at least one receptor molecular component that can recognize selectively a specific molecular information. The receptor component responds to a specific molecular information in changing in conformation and electron transfer, which results in information transduction as schematically shown in Fig.4. 

The proposed changes in conformation of residues 89—174 have led us to place this model (Govaerts et al, 2004) in the Refolding class, although the native disorder of residues 89-124 could equally place this model into the Natively Disordered class. 

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