Enzyme chemical modification

Classical approaches to chemical enzyme modification, however, often suffer from lack of regio-selectivity, which can yield heterogeneous and irreproducible enzyme mixtures. For example, preparation of methyl-chymotrypsin, -subtilisin or -trypsin using methyl sulfonate reagents, originally used to methylate the histidine of the... 

In a chemical enzyme-modification experiment conducted by E. F. Jansen and colleagues in 1949, chymotrypsin was incubated with 32P-Iabeled DFP and then hydrolyzed with a strong acid. Separation of the constituent amino acids revealed 1 mol of labeled Ophosphorylserine per 25,000 g of chymotrypsin. Since DFP is a potent inhibitor of the enzyme chymotrypsin, what might we infer about the amino acid side-chain composition of the active site ... 

The widely commercially exploited guar GaM has been the subject of some studies dealing with chemical or enzymic modifications aimed to extend the apphcation range of this polysaccharide. Specific oxidation on the C-6 position of the Galp side chain units was performed by /1-galactosidase [241,430]. 

The structural varieties of hemicelluloses offer a number of possibilities for specific chemical, physical, and enzymic modifications. Future advancements will be based on the synthesis of hemicellulose-based polymers with new functionalities and with a well-defined and preset primary structure both on the level of the repeating imit and the polymer chain. Hemicelluloses have also started to be attractive to synthetic polymer chemists as... 

Martirosova, E., Karpekina, T., El -Registan, G. Enzyme modification by natural chemical chaperons of microorganisms. Microbiology, Vol.73, No.5, (August 2004), pp. 609-615, ISSN 1350-0872... 

The following factors appear to control the emulsification properties of milk proteins in food product applications 1) the physico-chemical state of the proteins as influenced by pH, Ca and other polyvalent ions, denaturation, aggregation, enzyme modification, and conditions used to produce the emulsion 2) composition and processing conditions with respect to lipid-protein ratio, chemical emulsifiers, physical state of the fat phase, ionic activities, pH, and viscosity of the dispersion phase surrounding the fat globules and 3) the sequence and process for incorporating the respective components of the emulsion and for forming the emulsion. 

The search for active sites of the enzyme, by chemical and enzymic modifications has been extensively carried out since 1959 and was recently reviewed in detail (11). Only a short summary will be presented here. 

Other methods of stabilization include chemical or carbohydrate modification of enzymes. Modifications of reactive groups on proteins without insolubilization has been used to enhance stability in solution. Grafting of polysaccharides or synthetic polymers, alkalation, acetylation and amino acid modification have all been reported (5)... 

There has been much work designed to study structure-function relationships in GH by producing variants of the hormone by chemical or enzymic modification [1]. Now... 

Figure 3.11 shows the chemical deposition process of GOx enzyme assembled 2-mercaptoethanol on gold that was previously modified by cobalt tetracarboxylic acid chloride phthalocyanine self-assembled monolayer gold. Electrochemical biosensor was introduced in the following steps pretreatment hydrolysis functionalized surface -> enzyme modification. Shervedani and his coworkers reported a similar... 

Sometimes, the most convenient method of preparation of the labeled sugar required is by chemical or enzymic modification of a more readily available, or commercially available, sugar. Thus, D-ribose-3-t has been prepared from l,2 5,6-di-0-isopropylidene-a-D-allofuranose-3-t by way of 1,2-O-isopropylidene-a-D-allofuranose-3-t, followed by periodate oxidation, and reduction.52... 

Chemical modification Enzyme modification Compounding Wetting agents... 

Advances in genetic and chemical enz)me modifications, enzyme immobilisation and enzymatic reactions in organic solvents, have increased the actual use and potential of enzymes in the production of industrial chemicals. Enzyme immobilisation, in particular, has proved to be a valuable approach to the use of enz5mes in chemical synthesis. The term denotes eirzymes that are physically confined or localised in a defined region in space with retention of their catalytic activities. A detailed consideration of immobilisation techniques is beyond the scope of this chapter the subject is covered adequately in the BKDTOL text entitled Technological Applications of Biocatalysts. ... 

Haard, N.F., Enzymic modification in food systems, in Chemical and Functional Properties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Lancaster, PA, 2001, p. 155. 

Most of the enzyme modification reactions, and hence of the coupling reactions, are nucleophilic reactions, in particular bimolecular nucleophilic substitution reactions following an 5 2-type mechanism. Therefore, the chemical reactivity is basically a function of nucleophilicity of the amino acid side chain. Following the overall nucleophilic order of Edwards and Pearson [22], the sulfhydryl group of cysteine is the most potent nucleophile in the protein, especially in its thiolate form. 

Many of the side chain groups of amino acids in proteins are much more reactive in the protein than in an isolated amino acid state, although the reverse is usually the case. In these particular proteins there is probably a composite effect of many factors in the protein structure this greatly increases the reactivity of such a particular amino acid side chain to a chemical reagent. In many cases this hyperreactivity can be utilized in chemical modifications. Many such highly reactive groups are found to be related to the active sites of enzymes. Modifications of active sites will be discussed in more detail below. 

In the simplest of terms, manipulation of polyketide and nonribosomal peptide components involves alteration of materials, tools, or both. From a chemical standpoint, modification of building blocks can ideally result in structures limited only by our imagination. Biologically, genetic control over biosynthetic machinery could allow, theoretically, for boundless reprogramming capabilities. Realistically, insight from both perspectives will be required as enzyme selectivity and reactivity can impede combinatorial prospects. 

---