NAD polymerization

Nonaqueous dispersion (NAD) polymerization, 20 82 of methacrylic ester polymers, 16 289 Nonaqueous media, separations in, 21 654r-656... 

In conclusion, although the old question concerning the diradical or concerted process of the rDA is still under investigation [96], it seems that the initiation of the NAD polymerization is in any case the rDA reaction. 

Examples of dispersion polymerizations using macromonomers are summarized in Table 4. Non-aqueous dispersion (NAD) polymerization of polar... 

Oxidation of P-nicotinamide adenine dinucleotide (NADH) to NAD+ has attracted much interest from the viewpoint of its role in biosensors reactions. It has been reported that several quinone derivatives and polymerized redox dyes, such as phenoxazine and phenothiazine derivatives, possess catalytic activities for the oxidation of NADH and have been used for dehydrogenase biosensors development [1, 2]. Flavins (contain in chemical structure isoalloxazine ring) are the prosthetic groups responsible for NAD+/NADH conversion in the active sites of some dehydrogenase enzymes. Upon the electropolymerization of flavin derivatives, the effective catalysts of NAD+/NADH regeneration, which mimic the NADH-dehydrogenase activity, would be synthesized [3]. 

Polymerization Binder for M48 Decoy Flares , NAD-RDTR No 232 (1973) 60) R.C. Harris,... 

A platinum disk electrode was electrolytically platinized in a platinum chloride solution to increase the surface area and enhance the adsorption power. The platinized platinum electrode was then immersed in a solution containing 10 mg ml l ADH. 0.75 mM and 6.2 mM NAD. After sufficient adsorption of these molecules on the electrode surface, the electrode was transferred into a solution containing 0.1 M pyrrole and 1 M KC1. Electrochemical polymerization of pyrrole was conducted at +0.7 V vs. Ag/AgCl. The electrolysis was stopped at a total charge of 1 C cm 2. An enzyme-entrapped polypyrrole membrane was deposited on the electrode surface. 

Many enzymes require the participation of dissociable coenzymes such as NAD+, NADP+ or ATP for their catalytic activities. The use of coenzymes to activate immobilized enzymes on a large scale is hampered by their relatively low stability and high cost. Attempts are therefore being made to stabilize the coenzymes and to find suitable means for their continuous regeneration. The principal approach has been to covalently attach a co-enzyme to a polymeric water-soluble matrix, thus making the co-enzyme, like the enzyme, potentially reusable (9,10). 

Figure 2 The actin-ADP-ribosylating toxins, (a) Molecular mode of action. The actin-ADP-ribosylating toxins covalently transfer an ADP-ribose moiety from NAD+ onto Arg177 of G-actin in the cytosol of targeted cells. Mono-ADP-ribosylated G-actin acts as a capping protein and inhibits the assembly of nonmodified actin into filaments. Thus, actin polymerization is blocked at the fast-growing ends of actin filaments (plus or barbed ends) but not at the slow growing ends (minus or pointed ends). This effect ultimately increases the critical concentration necessary for actin polymerization and tends to depolymerize F-actin. Finally, all actin within an intoxicated cell becomes trapped as ADP-ribosylated G-actin.

This enzyme [EC 2.4.2.30] (also referred to as NAD+ ADP-ribosyltransferase, poly(ADP) polymerase, poly-(adenosine diphosphate ribose) polymerase, and ADP-ribosyltransferase (polymerizing)) catalyzes the reaction of NAD+ with [ADP-D-ribosyl] to produce nicotinamide and [ADP-D-ribosyl]( + i). The ADP-d-ribosyl group of NAD+ is transferred to an acceptor carboxyl group on a histone or on the enzyme itself, and further ADP-ribosyl groups are transferred to the 2 -position of the terminal adenosine moiety, building up a polymer with an average chain length of twenty to thirty units. 

Figure 20-23 (a) Surface plasmon resonance spectrum of sensor coated with molecularly imprinted polymer that selectively binds NAD+. (b) Response of sensor to four similar molecules shows largest response to NAD+, which was the template for polymerization. [From O. A. Raitman. V. I. Chegel, a B. Kharitonov. M. Zayats. E. Katz, and I. Winner. Analysis of NAD(P) and NAD(P)H Cofactors by Means of Imprinted Polymers Associated with Au Surfaces A Surface Plasmon Resonance Study. Anal. CNm. Ada 2004,504. 101.]... 

DNA polymerase I then uses its polymerizing and 5 to 3 exonuclease activities to remove the RNA primer and fill in this sequence with DNA. Because Pol I is not very processive, it falls off the lagging strand after a relatively short-length synthesis. DNA polymerases can t seal up the nicks that result from the replacement of RNA primers with DNA. Instead, another enzyme, DNA ligase, seals off the nicks by using high energy phosphodiester bonds in ATP or NAD to join a free 3 hydroxyl with an adjacent 5 phosphate. 

Shimizu et al. used simple rhodium-aqua ions (Rh3+) immobilized onto polymer-modified electrodes to perform the electrochemical reduction of NAD+ [114]. Rh3+ was loaded onto polymeric anion doped-polypyrrole membranes coated on the surface. Electrochemical reduction of NAD+ with immobilized Rh3+ was performed at —0.85 V, where Rh3+ was reduced to Rh+. NADH was produced without detectable formation of NAD-dimers. 

In this process, the monomer and iniliator are soluble in the continuous phase and the polymer particles, which precipitate as they are produced, are stabilized against coagulation by dispersants that comprise di fferent segments that are respectively soluble and insoluble in the continuous phase. Dispersion polymerizations have been used successfully as an alternative to solution polymerization of vinyl polymers for application as surface coatings. In that case the diluents are usually aliphatic hydrocarbons, and the process acronym is NAD [for nonaqueous dispersion]. 

Purines and pyrimidines are derived largely from amino acids. The biosynthesis of these precursors of DNA, RNA, and numerous coenzymes will be discussed in detail in Chapter 25. The reactive terminus of sphingosine, an intermediate in the synthesis of sphingolipids, comes from serine. Histamine, a potent vasodilator, is derived from histidine by decarboxylation. Tyrosine is a precursor of the hormones thyroxine (tetraiodothyronine) and epinephrine and of melanin, a complex polymeric pigment. The neurotransmitter serotonin (5-hydroxytryptamine) and the nicotinamide ring of NAD + are synthesized from tryptophan. Let us now consider in more detail three particularly important biochemicals derived from amino acids. 

Gorton et al. reported carbon paste electrodes based on Toluidine Blue O (TBO)-methacrylate co-polymers or ethylenediamine polymer derivative and NAD" " with yeast alcohol dehydrogenase for the analysis of ethanol [152,153] and with D-lactate dehydrogenase for the analysis of D-lactic acid [154]. Use of electrodes prepared with dye-modified polymeric electron transfer systems and NAD+/NADH to detect vitamin K and pyruvic acid has also been reported by Okamoto et al. [153]. Although these sensors showed acceptable performances, insensitivity to ambient oxygen concentration, sensor stability and lifetime still need to be improved to obtain optimal dehydrogenase based enzyme biosensors. 

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