Conformational movement

The catalytic subunit of cAPK contains two domains connected by a peptide linker. ATP binds in a deep cleft between the two domains. Presently, crystal structures showed cAPK in three different conformations, (1) in a closed conformation in the ternary complex with ATP or other tight-binding ligands and a peptide inhibitor PKI(5-24), (2) in an intermediate conformation in the binary complex with adenosine, and (3) in an open conformation in the binary complex of mammalian cAPK with PKI(5-24). Fig.l shows a superposition of the three protein kinase configurations to visualize the type of conformational movement. 

The surface concentration of polymeric segments relaxed by conformational movements on the borders of the oxidized regions a) can be expressed as follows ... 

X-ray structures of mitochondrial 6ci complexes from three different sources (113, 124, 125) have found the b- and c-type hemes at roughly identical positions, whereas the Rieske protein was seen in different places as a function of crystal space group and presence or absence of inhibitors of the enzyme. This fact was interpreted to suggest a long-range conformational movement of the Rieske protein during turnover of the complex. The range of observed positions of the Rieske protein indicated that the soluble domain can move like a... 

Perhaps the most Important effect of conformational variations In electron transfer reactions would be to alter the distances and the relative orientations of donors and acceptors. In photosynthetic RC s, where the primary donors and acceptors lie within 4-5A of each other ( ), small structural displacements (, 5A) may significantly affect rates of back reactions. If they occur rapidly (24), (Conformational movements on a picosecond time scale are not Inconsistent with resonance Raman data on photo-dlssoclated heme-CO complexes (25)), On a longer time scale, protein rearrangements triggered by and propagating from the chromophores may also help subsequent reactions such as the transport of protons that Is Initiated by the primary photochemical event In the R,C, (26),... 

The conformational movements associated with formation of open structures affect the positions of several catalytically important residues in the active site. The I helix bulge, which controls the water structure about the heme, and the catalytically relevant Asp251 and Thr252 residues are displaced into positions similar to those observed on dioxygen binding (Fig. 7) [9]. In... 

Proteins that bind the major groove but do not perturb the normal B-DNA structure can enhance CT efficiency in DNA. This was demonstrated by using the restriction endonuclease PvuII and the transcription factor ANTP [17]. As a result of the binding of proteins, the DNA conformation is stiffened, the conformational movements are reduced, and, as a result, CT is facilitated. In contrast with R.PvuII and ANTP, the TATA-box binding protein induces two 90° bends in the DNA... 

From the above results it can be inferred that sulfinyl ethylenes are not good dienophiles because of their low reactivity and poor stereoselectivity. In order to improve both of these factors, different electron-withdrawing groups (able to increase dienophilic reactivity and to restrict conformational movement around the C-S bond, thus improving the stereoselectivity) were incorporated into the double bond. They are presented in the sections below, classified according to the number and kind of the additional activating groups present in the vinyl sulfoxide moiety. 

Viscotropic effects in cells cultured at a single temperature may be indicative of effects that result from immediate temperature-dependent changes in lipid order and from subsequent adaptive alterations in lipid composition. Acute decreases in temperature increase static order and thereby increase resistance to conformational movements however, the compensatory decrease in intrinsic membrane order in cold-adapted or cold-acclimatized organisms (figure 7.21) resulting from changes in composi-... 

For main-chain acrylic radicals, created in solution at room temperature and above, the presence of a superposition of conformations or Gaussian distributions is unlikely. Polymers undergo conformational jumps on the submicrosecond timescale, even in bulk at room temperamre. ° The first two theories above require that the radicals be fairly rigid with little (Gaussian distribution) or no (superposition of static conformations) movement around the Cp bond. The main-chain radical is sterically hindered but still quite flexible, and a dramatic change in the hybridization at Ca is unlikely. We have approached our simulations with the hyperfine modulation model. 

In any of the electromechanical devices, strong electric fields act on the permanent or induced dipoles present along the polymeric chains promoting coulombic interactions, forcing conformational movements on the polymeric chains and concomitant macroscopic changes of volume, which relax in the absence of the electric field. Similar coulombic interactions occur when a solvent and ions are present, giving electrokinetic (electroosmotic and electrophoretic) processes. So, electrostatic and mechanical models applied to polymeric materials are required to model the attained responses. No chemical reaction is required for the actuation of those devices. 

Both the theoretical model and this basic molecular actuator include electric pulses, ions and water interchanges between the polymer and the solution, chemical reactions, stimulation of the conformational movements along polymeric chains, and changes in the inter- and intramolecular interactions. Those processes occurring in soft and wet materials mimic, at the molecular level, the consecutive events involved in the actuation of a natural anisotropic muscle. 

The latter facilitates conformational movements during catalysis (such as the induced fit , see below) thereby underlining the pronounced dynamic character of enzyme catalysis. Besides the main polyamide backbone, the only covalent bonds are -S-S- disulfide bridges. Enzymes are intrinsically unstable in solution and can be deactivated by denaturation, caused by increased temperature, extreme pH, or an unfavorable dielectric environment such as high salt concentrations. 

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