Chemical modification, proteins

Protein chemical modification is a problem-solving technique in research and technology. Modifications also occur in natural deteriorations. Generally these modifications are with the most reactive side chains and are predominantly oxidations, reductions, and nucleophilic and electrophilic substitutions. Deteriorations include peptide bond scissions, racemizations, fi-eliminations, and formation of products by the reaction of proteins with added chemicals. Proteins are modified intentionally for structure-function relationship studies or for development of new and improved products. Although appearing quite varied, the techniques used in pharmacological, food and feed, or other industrial areas differ more operationally than from major differences in the levels of chemical sophistication that are used. 

In relation to food proteins, chemical modification has been studied for several purposes, i.e. to block reactive groups involved in deteriorative reactions to improve nutritional properties, to enhance digestibility to impart thermal stability to modify physicochemical properties to facilitate study of structure-function relationships and to facilitate separation, processing and refining of proteins (1,2,10,19,20,24). 

The external environment has a great effect on the structure of most proteins. Chemical modification can change the response of a protein to its environment, and indeed this may be a purpose of many modifications that would be useful for food proteins. Denaturation is any change from the natural or so-called native state (18). It is also frequently defined as a change from an ordered to a disordered state. Operationally, many denaturations are irreversible, although the reversibility of the individual processes leading to the extremes of denaturation is a fact. In other words, denaturations are reversible, and it is only the interplay of many factors and subsequent reactions occurring after denaturation that make it practically impossible to return to the native state. 

Protein engineering. 2. Proteins—Surfaces. 3. Proteins— Chemical modification. I. Magdassi, Shlomo. 

Both 4 a and 4b result in a change in the active conformation of the enzyme protein. Chemical modification causes a change in the equilibrium protomers oligomers, leading to the establishment or abolition of quatemery structure. 

Another popular series of organic reagents for protein chemical modification is the isothiocyanates. They have found numerous applications in peptide and protein chemistry [92]. The best known examples are phenyl isothiocyanate 54 (Edmaris sequencing reagent) and fluorescein isothiocyanate 55. 

E. Basle, N. Joubert, and M. Pucheault, Protein chemical modification on endogenous amino acids, Chem. Biol, 17,213-227,2010. 

Purification. Hemoglobin is provided by the red blood ceU in highly purified form. However, the red ceU contains many enzymes and other proteins, and red ceU membranes contain many components that could potentially cause toxicity problems. Furthermore, plasma proteins and other components could cause toxic reactions in recipients of hemoglobin preparations. The chemical modification reactions discussed herein are not specific for hemoglobin and may modify other proteins as well. Indeed, multifimctional reagents could actually couple hemoglobin to nonhemoglobin proteins. 

Introduction of heme residues and different artificial receptors in protein molecules in chemical modification of structures and functions of proteins by the cofactor reconstruction method 99Ef0539. 

There are a number of practical problems involved with using polysaccharides as vaccines as there are frequently too many different chemotypes for it to be practicable to prepare a vaccine. In some cases a limited number of serotypes are the dominant cause of infection and it may then be possible to produce vaccines. A major problem is the poor immune response elicited by polysaccharide antigens, which may in some cases be improved by chemical modification. This is (fie case for vaccines for Haemophilus influenzae type b (a causative agent of meningitis), where the antigenicity of the polysaccharide can be increased by coupling to proteins. 

Binding to transport proteins may be of particular interest, since binding not only assays the affinities of the binding site on the transporter protein but also the translocation equilibria [67], In terms of enzyme catalysis, a transport protein transforms a substrate, a molecule located at one side of the membrane, into a product, the same molecule at the other side of the membrane, without chemical modification. Substrate must bind to a particular conformation of the enzyme with the binding sites accessible only from, for example, the outside. Similarly, the release of the product has to occur from a conformation which opens the binding site to the inside only this implies at least one transition step between the two types of conformations (see Fig. 

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