Instability covalent process

A difficult problem in utilizing enzymes as catalysts for reactions in a non-cellular environment is their instability. Most enzymes readily denature and become inactive on heating, exposure to air, or in organic solvents. An expensive catalyst that can be used only for one batch is not likely to be economical in an industrial process. Ideally, a catalyst, be it an enzyme or other, should be easily separable from the reaction mixtures and indefinitely reusable. A promising approach to the separation problem is to use the technique of enzyme immobilization. This means that the enzyme is modified by making it insoluble in the reaction medium. If the enzyme is insoluble and still able to manifest its catalytic activity, it can be separated from the reaction medium with minimum loss and reused. Immobilization can be achieved by linking the enzyme covalently to a polymer matrix in the same general manner as is used in solid-phase peptide synthesis (Section 25-7D). 

The driving force for the development of chemiluminescence-based assays (as well as any other optical or electrical detection methodology) is the replacement of radiolabels both for safety reasons and because of their intrinsic instability. Because the earliest high sensitivity immunoassays utilized antibodies with covalently attached as the label, this has served as a yardstick against which all subsequent assay technologies are measured. For this reason, it is important to understand the detection limits for I. Radioactive iodine is a y-emitter that eventually decays to a stable isotope of lead. The decay process exhibits first-order kinetics so that we can write... 

There are two main PAHs metabolization process in the cells, which lead to damages in the DNA. One activation via is characterized by the dihydrodiol epoxides formation, that bind, covalently, to amino heterocyclics groups of purine bases, to form stable adducts. Another via involves the formation of cation radicals, which bind to the N7 or C8 of the purine bases to form instable adducts and generate apurine sites in the DNA, by spontaneous depurination (Melendez-Colon et al., 1999). 

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