Enzymes chemically modified

R.M. Ianniello and A.M. Yacynych, Immobilized enzyme chemically modified electrode as an amperometric sensor. Anal. Chem. 53, 2090-2095 (1981). 

In a similar way to mediators, enzymes may be covalently bound to electrode surfaces, thus giving enzyme-chemically modified electrodes (ECME). When enzymes and mediators are coimmobilized, addition of auxiliary substances during the measuring process can be avoided a reagentless measuring regime becomes feasible (Fig. 19). 

ADP AFP ab as ALAT AP ASAT ATP BQ BSA CEH CK CME COD con A CV d D E E EC ECME EDTA EIA /e FAD FET FIA G GOD G6P-DH HBg HCG adenosine diphosphate a-fetoprotein antibody antigen alanine aminotranferase alkaline phosphatase aspartate aminotransferase adenosine triphosphate benzoquinone bovine serum albumin cholesterol ester hydrolase creatine kinase chemically modified electrode cholesterol oxidase concanavalin A coefficient of variation (relative standard deviation) layer thickness diffusion coefficient enzyme potential Enzyme Classification enzyme-chemically modified electrode ethylene diamine tetraacetic acid enzyme immunoassay enzyme loading factor flavin adenine dinucleotide field effect transistor flow injection analysis amplification factor glucose oxidase glucose-6-phosphate dehydrogenase hepatitis B surface antigen human chorionic gonadotropin... 

H. J. Wieck, Characterization of Immobilized Enzyme Chemically Modified Electrodes and Their Application in Flow Injection Analysis. Diss. Abstr. Int. B., 44 (1983) 1449. 

J. A. Osborn, A. M. Yacynych, and D. C. Roberts, A Flow-Injection System for Assay of the Activity of an Immobilized Enzyme Chemically-Modified Electrode. Anal. Chim. Acta, 183 (1986) 287. 

In 1988, a pioneering work dealing with electrode characteristics of an immobilized enzyme chemically modified electrode based on bilayer-film coating for amperometric determination of glucose was reported. In this work, a substrate was coated with two kinds of polymeric films in a bilayer state, that is, first with the cobalt tetrakis(o-aminophenyl)porphyrin polymer film and then with the enzyme film consisting of bovine serum albumin and glucose oxidase that were... 

Such lECMEs (immobilized enzyme chemically modified electrodes) can be used both as potentiometric and amperometric sensors [136]. The covalent bonding of enzyme causes the optimal orientation of electroactive enzyme centers toward the electrode surface. Direct transfer of electrons between bound enzyme and the carbon of an lECME was proved [137, 138]. The large active surface and very thin enzyme layer of lECMEs are the reasons for higher sensitivity, lower detection limit, broader linear concentration range and faster response than in the case of other enzyme sensors. 

In so-called ping-pong reactions products are released in a stepwise fashion. In a two-substrate reaction, the first substrate (S,) binds to the enzyme E and a product (Pi) is released, leaving the enzyme chemically modified (denoted E ), perhaps by a fragment of the substrate. Then the second substrate (S2) binds to the modified enzyme and is processed into a second product, P2, returning the enzyme to its native form. The scheme can be summarized as follows ... 

In most cases, hoUow fibers are used as cylindrical membranes that permit selective exchange of materials across their waUs. However, they can also be used as containers to effect the controUed release of a specific material (2), or as reactors to chemically modify a permeate as it diffuses through a chemically activated hoUow-fiber waU, eg, loaded with immobilized enzyme (see Enzyme applications). 

The other general possibility is that one substrate. A, binds to the enzyme and reacts with it to yield a chemically modified form of the enzyme (E ) plus the product, P. The second substrate, B, then reacts with E, regenerating E and forming the other product, Q. 

Inhibitors of the catalytic activities of enzymes provide both pharmacologic agents and research tools for study of the mechanism of enzyme action. Inhibitors can be classified based upon their site of action on the enzyme, on whether or not they chemically modify the enzyme, or on the kinetic parameters they influence. KineticaUy, we distinguish two classes of inhibitors based upon whether raising the substrate concentration does or does not overcome the inhibition. 

Walsh, C.T., Chen, H., Keating, T.A. et al. (2001) Tailoring enzymes that modify nonribosomal peptides during and after chain elongation on NRPS assembly lines. Current Opinion in Chemical Biology, 5 (5), 525-534. 

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. 

Y. Degani and A. Heller, Direct electrical communication between chemically modified enzymes and metal electrodes. I. Electron transfer from glucose oxidase to metal electrodes via electron relays, bound covalently to the enzyme. J. Phys. Chem. 91, 1285-1289 (1987). 

J. Pei and X. Li, Amperometric glucose enzyme sensor prepared by immobilizing glucose oxidase on CuPtC16 chemically modified electrode. Electroanalysis 11, 1266-1272 (1999). 

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. 

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