The Protein Effect

Natural rubber vulcanizates and their unvulcanized precursors differ significantly from synthetic c/5-l,4-polyisoprenes in the case of many properties, for example those listed in columns A and B below. 

Modulus of vulcanizate Heat build-up during flexing of vulcanizate 

Green strength of unvulcanized compound Festoon sagging of unvulcanized compound Hot tear strength of vulcanizate 

It has been found (Gregg and Macey, 1973) that the difference between the natural and the synthetic polymers in the column A 

Column B properties are not related to this protein effect and are generally associated with the lower structural perfection of synthetic materials (e.g. presence of 3,4- structures). 

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Whether the protein effect is considered important depends heavily on the type of process that is being studied. If the target is to understand the color-tuning effects of... 

As briefly mentioned above, the reduced form of MMO reacts with oxygen to initiate substrate oxygenation. To further analyze the protein effects on this reaction, the dioxygen-binding step was treated with two-layer ONIOM (B3LYP Amber) [25], The overall setup was similar to the one used for evaluating active-site geometries. 

For the present reaction, the presence of surrounding protein only marginally affects the barrier (it increases by 0.7 kcal/mol). A possible reason for the small protein effects could be that in the present model, the active site is not deeply buried inside the enzyme instead it is located on the interface of two monomers. Still, addition of the protein environment had effects on the active-site geometry. The reason this does not affect the total barrier height is that when comparing transition state and reactant, the protein effect appears to be relatively constant. 

Fig. 14.5. Experimental rejection (o) and theoretical prediction of the critical pressure for filtration of BSA in 0.001 M NaCI solution at pH 9 at a membrane of mean pore diameter 84 nm. Rejection is high below the critical pressure as electrical double layer repulsion prevents the protein (effective spherical diameter 6nm) from entering the membrane pores. As the critical pressure is approached, hydrodynamic forces increase and drive the...

Several computational models were employed in our study [35], Model I included a chromophore in gas-phase (Figure 4-10(a-d)). Model II additionally involved a point-charge model for protein electrostatic potential. In Model HI, the atoms in the active site (Figure 4-10(f)) were treated by quantum mechanics, and the rest of the protein effect was treated by the point-charge model. The structures used in Models... 

An aromatic amino acid residue of a protein may be buried deep within the three dimensional structure of the protein, effectively shielded from the surrounding medium or it may lie on the surface highly exposed to the solvent medium. Furthermore, protein molecules in vivo are found in many different types of media ranging from the aqueous soup of cell cytoplasm to the highly ordered crystalline type environments of structural proteins. Thus, it is necessary to examine the luminescence properties of the aromatic amino acids in a wide variety of solvent media in order to begin to interpret protein emission characteristics. 

They concluded that ionizable groups on the surface, where they tend to be found, do not contribute significantly to the protein dielectric constant deep in the interior of the protein. This is partly because these surface residues tend to be well hydrated, thereby weakening their electrosatic interaction with points deep in the protein. Effects of ionized residues are more likely to be highly position dependent. That is, for points close to an ionized residue, the effective protein dielectric constant would be predicted to be higher than points farther in the interior of the protein. 

The emphasis in the study of protein adsorption has been the composition of the adsorbed layer, rate of adsorption, and possible changes, such as denaturation of the proteins effected by the adsorption process. Such studies, in relation to surface character, surface thrombogenicity, and platelet adsorption, have primarily... 

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