Chemically modified proteins applications

Direct electron transfer between redox proteins and metal electrodes has many advantages with respect to analytical applications. Hill and coworkers have pointed out the similarities between heterogeneous electron transfer reactions of proteins at electrodes and catalysis. The sequence of events at the electrode include 1) diffusion of reactant protein to the electrode surface 2) adsorption of the protein in an orientation suitable for electron transfer 3) electron transfer 4) dissociation of the protein from the electrode surface and 5) diffusion of the protein away from the surface. If all these requirements are not met, well behaved redox activity will not be observed. There have been various approaches to accomplishing reversible redox reactions in proteins based upon these requirements. Hill and coworkers have focused on the second step and have shown by their elegant promoter studies that the correct orientation of the protein at the electrode is crucial for rapid electron transfer. Others have utilized mediator-type electrodes or chemically modified proteins. ... 

By combining bacterial expression and chemical synthesis Ras constructs with the properties of the post-translationally modified protein can be generated. These hybrid proteins can insert into artifical and biological membranes, have been proven to be efficient tools for biochemical, biophysical and biological experiments and can be synthesized in large amounts. Principally the same method is applicable to many of the Ras-related GTP-binding proteins or the y-subunit of heterotrimeric G proteins. 

The are several clearance and toxicological aspects that have to be considered in the drug discovery process such as metabolic stability, enzyme selectivity, CYP inhibition and type of inhibition. Among these factors, the prediction of the site of metabolism has become one of the most successful parameters for prediction. The knowledge of the site of metabolism enhances the opportunity to chemically modify the molecule to improve the metabolic stability. There are several approaches based on database mining, chemical reactivity, protein interaction or both that have been developed for the prediction of this property, with different degree of success and applicability. 

The efficacy of CE separation depends considerably on the type of capillary. Fused-silica capillaries without pretreatment are used most frequently. Its outside is coated with a polymer layer to make it flexible and to lessen the occurrence of breakage. The polymer coating has to be dissolved with acid or burned away at the detection point. Capillaries with an optically transparent outer coating have also found application in CE. The objectives of the development of chemically modified capillary walls were the elimination of electro-osmotic flow and the prevention of adsorption on the inner wall of the capillary. Another method to prevent the adsorption of cationic analyses and proteins is the use of mobile phase additives. The modification of the pH of the buffer, the addition of salts, amines and polymers have all been successfully employed for the improvement of separation. 

The protein fraction is filtered and dried to become high (60%) protein content com gluten meal. The starch slurry can be dewatered and dried to produce regular com starch. Dry starch can be sold as is or heat treated in the presence of acid catalysts to produce dextrins. Or, it is chemically modified before dewatering and drying to produce modified starches used in food and industrial applications. Lastly, it can be hydrolyzed to produce com sweeteners. 

Cnzyme-catalyzed modifications of proteins deserve much more work and therefore must be considered as an important field for further scientific investigations. In spite of the prolific research carried out in this area during the past three decades, a number of enzymatic modifications not only are poorly investigated or understood but attempts to apply them to food protein systems are nonexistent. The fundamental aspects of enzymatic modification of proteins are of interest since potential applications for nutritional and functional improvements of food proteins appear to be numerous and promising. Enzymatic and chemical modifi-... 

In the analysis of proteins in forensic applications, the chemical modifications that occur to proteins, posttranslationally and nonenzymatically, are of primary importance. These chemical changes are a result of chemical reactions between side chains of the protein and reactive groups of metabolites and/or exogenous toxicants, including drugs present in extracellular fluid such as serum. The analytical accessibility of these modified proteins depends on their rate of turnover. For example, those with a slow turnover rate will be long-lived, and such problems will be much more easy to identify than those with faster turnover rates. 

The main drawback to the widespread use of polymer-polymer aqueous two-phase extraction has been the high cost of fractionated dextran. Crude dextran has been used with some success for the purification of enzymes but is much too viscous for many applications. Conversely, polymer-salt systems have relatively low viscosities, separate rapidly, and are inexpensive. Unfortunately, they lack selectivity and cannot be used for affinity partitioning in most cases since the high salt concentrations interfere with the protein-ligand interaction. The starch derivatives are reasonable alternatives for bottom phase polymers but have been hampered by low solubilities and the tendency for gel formation. Tjemeld has reported that chemically modified starches i.e. hydroxypropyl starch... 

---