Enzymes — artificial

PC. Marijuan, Enzymes, artificial cells and the nature of biological information, BioSystems, 35, 167-170 (1995). 

Nanobarcodes Nanoemulsions Nanofibers Nanoparticles Nanoshells Carbon nanotubes Quantum dots Artificial binding sites Artificial antibodies Artificial enzymes Artificial receptors Molecularly imprinted polymers Cell simulations and cell diagnostics Cell chips Cell stimulators... 

Artificial cells have been used in hereditary enzyme defects, including our earliest use of a replacement for catalase in acatalasemic mice. This also has been studied for asparagine removal in the treatment of leukemia in animals."" We used phenylalanine ammonia lyase artificial cells in phenylketonuria rats." Later, we found an extensive enterore-circulation of amino acids in the intestine." This allows enzyme artificial cells to be used orally to selectively remove specific amino acids from the body, as in phenylketonuria." We also studied the oral administration of artificial cells containing xanthine oxidase." " This resulted in a decrease in systemic hypoxanthine in a pediatric patient with hypoxanthinuria (Lesch-Nyhan disease). 

One of the greatest obstacles in the successful modeling of the cytochrome P-450 system is the choice and control of electrons for the reductive activation of dioxygen. In our laboratory we began by designing a system that closely matched the environment of the native enzyme. Artificial bilayers in the form of polymerizied vesicles of 9 were utilized in an attempt to compartmentalize and separate the various components of the artificial enzyme system (Figure 7).2i... 

It also seems clear that specific interactions (which are used by natural enzymes) are missing from even the more sophisticated systems. This could be a problem if we want to mimic natural enzymes, or if we want to use (complex) model systems to understand the power of natural enzymes. But overall, there is no need for artificial design to replicate what we know about enzymes—artificial evolution might as well proceed toward a route unexplored by Nature. Although specific interactions are important for natural enzymes, or enzymes involved in metabolic pathways for which there needs to be discrimination, there are other processes for which such discrimination might not be crucial. Degradation of pollutants is an obvious... 

Figure C3.2.17. Diagram of a liposome-based artificial photosynthetic membrane showing the photocycle that pumps protons into the interior of the liposome and the CFqF j-ATP synthase enzyme. From [55],...

This experiment describes the use of a commercially available amperometric biosensor for glucose that utilizes the enzyme glucose oxidase. The concentration of glucose in artificial... 

There are thousands of breweries worldwide. However, the number of companies using fermentation to produce therapeutic substances and/or fine chemicals number well over 150, and those that grow microorganisms for food and feed number nearly 100. Lists of representative fermentation products produced commercially and the corresponding companies are available (1). Numerous other companies practice fermentation in some small capacity because it is often the only route to synthesize biochemical intermediates, enzymes, and many fine chemicals used in minor quantities. The large volume of L-phenylalanine is mainly used in the manufacture of the artificial dipeptide sweetener known as aspartame [22389-47-0]. Prior to the early 1980s there was httle demand for L-phenyl alanine, most of which was obtained by extraction from human hair and other nonmicrobiological sources. 

A compound which is a good choice for an artificial electron relay is one which can reach the reduced FADH2 active site, undergo fast electron transfer, and then transport the electrons to the electrodes as rapidly as possible. Electron-transport rate studies have been done for an enzyme electrode for glucose (G) using interdigitated array electrodes (41). The following mechanism for redox reactions in osmium polymer—GOD biosensor films has... 

An artificial metalloenzyme (26) was designed by Breslow et al. 24). It was the first example of a complete artificial enzyme, having a substrate binding cyclodextrin cavity and a Ni2+ ion-chelated nucleophilic group for catalysis. Metalloenzyme (26) behaves a real catalyst, exhibiting turnover, and enhances the rate of hydrolysis of p-nitrophenyl acetate more than 103 fold. The catalytic group of 26 is a -Ni2+ complex which itself is active toward the substrate 1, but not toward such a substrate having no metal ion affinity at a low catalyst concentration. It is appearent that the metal ion in 26 activates the oximate anion by chelation, but not the substrate directly as believed in carboxypeptidase. 

Reverse transcription is the copying of an RNA molecule back into its DNA complement. The enzymes that perform this function are called reverse transcriptases. Reverse transcription is used naturally by retroviruses to insert themselves into an organism s genome. Artificially induced reverse transcription is a useful technique for translating unstable messenger RNA (mRNA) molecules into stable cDNA. 

Neotame is an artificial sweetener designed to overcome some of the problems with aspartame. The dimethylbutyl part of the molecule was added to block the action of peptidases, enzymes that break the peptide bond between the two amino acids aspartic acid and phenylalanine. This reduces the availability of phenylalanine, eliminating the need for a warning on labels directed at people who cannot properly metabolize phenylalanine. 

In the enzyme design approach, as discussed in the first part of this chapter, one attempts to utilize the mechanistic understanding of chemical reactions and enzyme structure to create a new catalyst. This approach represents a largely academic research field aiming at fundamental understanding of biocatalysis. Indeed, the invention of functional artificial enzymes can be considered to be the ultimate test for any theory on enzyme mechanisms. Most artificial enzymes, to date, do not fulfill the conditions of catalytic efficiency and price per unit necessary for industrial applications. 

An interesting case in the perspective of artificial enzymes for enantioselective synthesis is the recently described peptide dendrimer aldolases [36]. These dendrimers utilize the enamine type I aldolase mechanism, which is found in natural aldolases [37] and antibodies [21].These aldolase dendrimers, for example, L2Dl,have multiple N-terminal proline residues as found in catalytic aldolase peptides [38], and display catalytic activity in aqueous medium under conditions where the small molecule catalysts are inactive (Figure 3.8). As most enzyme models, these dendrimers remain very far from natural enzymes in terms ofboth activity and selectivity, and at present should only be considered in the perspective of fundamental studies. 

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