Modified enzymes, properties

Glucose oxidase and D-amino acid oxidase can be chemically modified both in the presence and the absence of 2 M urea. At 2 M concentration urea interacts with proteins, opening their structure. Modification in the presence of 2 M urea was preferred because of superior reproducibility of the modified-enzyme-properties and because of superior electrochemical... 

Hydrolyzed Vegetable Protein. To modify functional properties, vegetable proteins such as those derived from soybean and other oil seeds can be hydrolyzed by acids or enzymes to yield hydrolyzed vegetable proteins (HVP). Hydrolysis of peptide bonds by acids or proteolytic enzymes yields lower molecular weight products useful as food flavorings. However, the protein functionaHties of these hydrolysates may be reduced over those of untreated protein. 

Abuchowski, A., Kazo, G.M., Verhoest Jr., C.R., van Es, T., Kafkewitz, D., Nucci, M.L., Viau, A.T., and Davis, F.F. (1984) Cancer therapy with chemically modified enzymes. Anti-tumor properties of polyethylene glycol asparaginase conjugates. Cancer Biochem. Biophys. 7, 175-186. 

There is another approach that is increasingly part of synthesis the use of enzymes as catalysts. This approach is strengthened by the new ability of chemists and molecular biologists to modify enzymes and change their properties. There is also interest in the use of artificial enzymes for this purpose, either those that are enzyme-like but are not proteins, or those that are proteins but based on antibodies. Catalytic antibodies and nonprotein enzyme mimics have shown some of the attractive features of enzymes in processes for which natural enzymes are not suitable. 

The recent literature in bioelectrochemical technology, covering primarily the electrochemical aspects of enzyme immobilization and mediation, includes few reports describing engineering aspects of enzymatic biofuel cells or related devices. Current engineering efforts address issues of catalytic rate and stability by seeking improved kinetic and thermodynamic properties in modified enzymes or synthesized enzyme mimics. Equally important is the development of materials and electrode structures that fully maximize the reaction rates of known biocatalysts within a stable environment. Ultimately, the performance of biocatalysts can be assessed only by their implementation in practical devices. 

Natural fats and oils can be used directly in products, either individually or as mixtures. In many cases, however, it is necessary to modify their properties, particularly their melting characteristics, to make them suitable for particular applications. Therefore, the oils and fats industry has developed several modification processes using enzyme technology. In particular, lipases (and lately cutinases), phospholipases and pectinases can be used for interesterification processes, ester syntheses and in olive-oil extraction. 

Another type of important selectivity is that between hydrolysis and transferase reactions (transesterification, transglycosylation, etc.) catalyzed by hydrolases. In this case, water can act both as a reactant and as a substance that modifies the properties of the enzyme. Effects of water as a reactant can be expected to be governed by the concentration or activity of water, as with other substrates. The effects of water as an enzyme modifier are considerably more difficult to predict. 

Fungal enzymes have been used for hundreds of year to prepare and modify foodstuffs. However, modern industrial enzyme technology probably started with Takamine (53) and his work with A. oryzae. Today many industrial enzymes used to modify functional properties of foods and food ingredients are of fungal origin (54). 

The original evidence for activation by modification of cysteine residues came from studies with 2,4-fluorodinitrobenzene (15). Incubation of the crystalline enzyme preparations with 4 equivalents of FDNB led to a marked increase in activity in the neutral pH range, together with a small decrease in the activity assayed at alkaline pH (Fig. 4). The modified enzyme showed two broad and nearly equal activity maxima one at pH 7.7 and the other at pH 9.0. When dinitrophenylation was carried out at pH 7.5, this change in catalytic properties was associated with the modification of only 2 of the 20 cysteine residues in the protein (16). These 2 highly reactive cysteine residues were found to be completely protected against the action of FDNB by addition of FDP. 

Application of Microorganisms and Enzymes for Modifying Allergenic Properties... 

In summary, enzymatic hydrolysis presents numerous possibilities to modify the properties of proteins. Several food-grade enzymes with different specificities are now available. The selection of an enzyme is mainly dictated by its cost, while the cost of an enzyme accounts for only a small percentage of the protein hydrolysate production cost. 

Time course experiments can be performed using different classes of control toxins to determine the length of exposure necessary to induce apoptosis or result in necrotic cell death. A toxin with properties that disrupt cell membranes will result in rapid necrotic cell death. Other chemicals may not become toxic until after conversion by modifying enzymes in the cytoplasm. In many cases, subpopulations of cells at different stages of the cell cycle may undergo cell death at different times. 

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