Enzymes chemical structure

On a different setup, Du et al. [31] cast sol-gel silica/gold nanoparticle nanocomposite films on a glassy carbon electrode, which was then impregnated with an acetylcholinesterase (AChE) enzyme (Figure 46.10). The construct was used as a biosensor for organophosphorus pesticide detection. In this system, gold nanoparticles not only offered a biocompatible microenvironment to retain the activity of adsorbed enzyme molecules but also acted as a wire to enhance the direct electron transfer rate between the enzyme active centers and the electrode surface, which otherwise would be blocked by the thick protein shell of the enzyme chemical structure. 

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]. 

L-Ascorbic acid, better known as vitamin C, has the simplest chemical structure of all the vitamins (Figure 18.30). It is widely distributed in the animal and plant kingdoms, and only a few vertebrates—humans and other primates, guinea pigs, fruit-eating bats, certain birds, and some fish (rainbow trout, carp, and Coho salmon, for example)—are unable to synthesize it. In all these organisms, the inability to synthesize ascorbic acid stems from a lack of a liver enzyme, L-gulono-y-lactone oxidase. 

The role of a cationic surfactant must be to provide a necessary hydrophobic and polarized environment for the molecule of luciferin for its luminescence reaction. In the case of a common luciferin-luciferase reaction, such an environment is provided by the enzyme luciferase. The chemical structures of PMs, as well as that of the natural luciferin, have not been determined yet (see the next section). 

Methotrexate (MTX, chemical structure shown in Fig. 1.) competitively inhibits the dehyrofolate reductase, an enzyme that plays an essential role in purine synthesis. The dehydrofolate reductase regenerates reduced folates when thymidine monophosphate is formed from deoxyuridine monophosphate. Without reduced folates cells are unable to synthesize thymine. Administration of N-5 tetrahydrofolate or N-5 formyl-tetrahydrofolate (folinic acid) can bypass this block and rescue cells from methotrexate activity by serving as antidote. 

Thienamycin (Fig. 5.5E) is a broad-spectrum /3-lactam antibiotic with high /3-lactamase resistance. Unfortunately, it is chemically unstable, although the TV-formimidoyl derivative, imipenem, overcomes this defect. Imipenem (Fig. 5.5E) is stable to most/3-lactamases but it readily hydrolysed by kidney dehydropeptidase and is administered with a dehydropeptidase inhibitor, cilastatin. Meropenem, which has yet to be marketed, is more stable than imipenem to this enzyme and may thus be administered without cilastatin. Its chemical structure is depicted in Fig. 5.5F. 

In order to investigate, and deduce, the complex carbohydrate structures of glycoproteins, it must be possible to release, and isolate, the oligosaccharide chain(s) from the glycoprotein. Following this, the structure is usually deduced by a combination of enzymic, chemical, and instrumental methods.34-36... 

The term hit confirmation, as we define it, involves three components reproducibility, confirmation of chemical structure, and confirmation of chemical purity. Confirmation of hit reproducibility requires that the subset of library compounds designated as hits in the primary screen be identified, that samples of each of these be obtained from the library bank (a process often referred to as cherry picking ), and that these samples be retested, at least once but preferably multiple times, to determine if they reproducibly confer an inhibition percentage of the target enzyme... 

Figure 7.9 Chemical structures of ligands of the enzyme PNP. (A) The substrate inosine, (B) the inosine and phosphate transition state, and (C) the transition state mimic inhibitor Imucillin H.

Most enzymes are very specific in their activity, and each chemical reaction in a living organism requires a specific enzyme. Their specificity arises from what is known as an active site, a location in the enzyme s molecule that has a shape matching that of a part of the molecule with which it reacts. The activity of the enzymes is affected by such factors as temperature and pH, each enzyme functioning best within a specific range of temperatures and pH. Outside this range the enzymes are structurally altered and their activity is either impaired or terminated. 

Upon entering the smooth muscle cell, Ca++ ions bind with calmodulin, an intracellular protein with a chemical structure similar to that of troponin. The resulting Ca++-calmodulin complex binds to and activates myosin kinase. This activated enzyme then phosphorylates myosin. Crossbridge cycling in smooth muscle may take place only when myosin has been phosphorylated. 

The variation of the chemical structures in both Type I and Type II compounds results from differences in both biosynthetic enzyme systems and their starting material. This topic, however, has been judiciously described in the chapter by R. Jurenka. While the grouping employed in this chapter is based on biosynthetic origin, some chemicals were involuntarily classified considering their functional groups more sizably than the origin. Incidentally, taxonomic information is important for insect pheromone research. In this chapter, the family name (with the common suffix -idae) is associated with the species name. For those species whose family name is not listed in Figs. 1 and 2, the superfamily name (with the common suffix -oidea) is associated. The subfamily name (with the common suffix -inae) is also described for the species in Tor-tricidae, Pyralidae, and Noctuidae. 

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