Proteins chelate effect

The chelate effect in proteins is also important, since the three-dimensional (3-D) structure of the protein can impose particular coordination geometry on the metal ion. This determines the ligands available for coordination, their stereochemistry and the local environment, through local hydrophobicity/hydrophilicity, hydrogen bonding by nearby residues with bound and non-bound residues in the metal ion s coordination sphere, etc. A good example is illustrated by the Zn2+-binding site of Cu/Zn superoxide dismutase, which has an affinity for Zn2+, such that the non-metallated protein can extract Zn2+ from solution into the site and can displace Cu2+ from the Zn2+ site when the di-Cu2+ protein is treated with excess Zn2+. 

Red blood cell labeling inhibition. Tobacco decreased the labeling of blood elements with technetium-99m and plasma proteins. This effect possibly resulted from either a direct or an indirect effect (reactive oxygen species [ROS]) of tobacco by oxidation of the stannous ion, possible damages caused in plasma membrane and/or possible chelating action on the stannous and/or pertechnetate ions . 

Ensembles 600 Enterokinase 480 Enthalpy 55 activation 56, 545-547 protein folding 509 -512 specific heat effects 511, 545 - 547 Enthalpy-entropy compensation 346 Enthalpy versus entropy in protein folding 509-512, 587, 599 Entropy 55, 68-72 activation 56, 545 -547 binding 324, 345 Boltzmann equation 510 chelate effect 345 configurational 510 configurational entropy of loops 535 effective concentration 68-72 equilibria on enzyme surface 118 hydrogen bond 338 hydrophobic bond 332, 510 importance in enzyme catalysis 72 importance in enzyme-substrate binding 72... 

In the first case, where the repressor protein is cut in half, the binding enthalpy for each part would be essentially half the enthalpy value for the intact repressor. The entropy would be less favorable (less positive) because of the chelation effect. As a result, the free energy would be less favorable (less negative). 

The chelate effect is distinct from multivalent binding modes that require receptor clustering [59]. Since the cell membrane is fluid, receptors are free to diffuse in two dimensions this mobility can lead to clustering of receptors. In such a system, the unliganded state of the saccharide-binding protein may not have the same distribution on the cell surface as the bound species. This clustering occurs with an entropy cost, but it does not require that the multidentate saccharide display match precisely the display of receptors on the cell surface. 

Although some structural features can influence the activity of the dendrimers [111], Roy s studies identified few major differences between dendrimers of different structure. If the dendrimers were acting via the chelate effect, changes in the distance between epitopes would be expected to perturb their functional affinity significantly. As stated above, however, the dendrimers crosslink their target proteins. Because small variations in their structure are unlikely... 

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