Conformational changes, Interaction

The regioselectivity benefits from the increased polarisation of the alkene moiety, reflected in the increased difference in the orbital coefficients on carbon 1 and 2. The increase in endo-exo selectivity is a result of an increased secondary orbital interaction that can be attributed to the increased orbital coefficient on the carbonyl carbon ". Also increased dipolar interactions, as a result of an increased polarisation, will contribute. Interestingly, Yamamoto has demonstrated that by usirg a very bulky catalyst the endo-pathway can be blocked and an excess of exo product can be obtained The increased di as tereo facial selectivity has been attributed to a more compact transition state for the catalysed reaction as a result of more efficient primary and secondary orbital interactions as well as conformational changes in the complexed dienophile" . Calculations show that, with the polarisation of the dienophile, the extent of asynchronicity in the activated complex increases . Some authors even report a zwitteriorric character of the activated complex of the Lewis-acid catalysed reaction " . Currently, Lewis-acid catalysis of Diels-Alder reactions is everyday practice in synthetic organic chemistry. 

In the structure of unphosphorylated phosducin that binds to Gpy, Ser 73 points towards the flexible loop of phosducin and not towards Gpy it is, therefore, accessible on the surface for phosphorylation. Phosphorylation of Ser 73 cannot lead to the direct disruption of the phosducin/GpY interaction. Rather, the structure suggests that phosphorylation may lead to conformational changes in the N-terminal domain of phosducin, especially in the flexible loop region, that could weaken or alter the phosducin/GpY interface. 

Wilson, I.A., 5tanfield, R.L. Antibody-antigen interactions new structures and new conformational changes. 

Protein-DNA backbone interactions determine DNA conformation Conformational changes of DNA are... 

The working hypothesis is that, by some means, interaction of an allosteric enzyme with effectors alters the distribution of conformational possibilities or subunit interactions available to the enzyme. That is, the regulatory effects exerted on the enzyme s activity are achieved by conformational changes occurring in the protein when effector metabolites bind. 

FIGURE 17.23 The mechanism of skeletal muscle contraction. The free energy of ATP hydrolysis drives a conformational change in the myosin head, resulting in net movement of the myosin heads along the actin filament. Inset) A ribbon and space-filling representation of the actin—myosin interaction. (SI myosin image courtesy of Ivan Rayment and Hazel M. Holden, University of Wiseonsin, Madison.)... 

Based on the information presented in the text and in Figures 25.4 and 25.5, suggest a model for the regulation of acetyl-CoA carboxylase. Consider the possible roles of subunit interactions, phosphorylation, and conformation changes in your model. 

In this sense it should be mentioned that (Ala)n is dissolved by hexafluorisopropanol (HFIP) without conformation change and that stretched fibers of (Leu) shrink in HFIP (20 °C) at about 60 % only by disorientation of (Leu)n molecules, because no conformation change occurs according to X-ray measurements 122,123). An interaction of the OH-group of the alcohol with the back-bone-CO-NH-groups is not very likely because, in this case, conformation changes should be observed. 

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