Extremophiles Extremophilic enzymes

Beyond their practical value, extremophile enzymes present scientists with a fundamental puzzle. Fike all molecular characteristics, their exceptional stability must originate in their chemical structures. However, it is not yet certain what structural features determine these properties. What is known is that in their active folded form, cold-resistant enzymes appear to have relatively fewer structure-stabilizing interactions between different parts of the amino acid chain. As a result, they remain more flexible at a lower temperature than ordinary enzymes but unfold and lose their activity more quickly as the temperature is raised. Conversely, heat-resistant enzymes seem to have a larger number of... 

Butler, L.G., Enzymes in non-aqueous solvents. Enzyme Microb. Technol., 1979,1, 253-259. Gerard A. Sellek, G.A. and Chaudhuri, J.B., Biocatalysis in organic media using enzymes from extremophiles. Enzyme Microb. Technol., 1999, 25, 471-482. 

Many scientists hope to discover other proteins that are stable at extremes of temperature, salt concentration, or pH. Biocatalysis can be a useful tool in a number of different applications. Just as Taq polymerase revolutionized PCR, other extremophilic enzymes might also serve as useful catalysts in commercially important reactions. T. aquaticus was a focus of much of the early work. In 1973, Stellwagen reported the isolation of a thermostable enolase from T. aquaticus YT-1. It was remarkably thermostable compared to enolases isolated from either yeasts or rabbit muscle cells. Taq... 

Mounting so cial, p olitical a nd e nvironmental p ressures on i ndustry t o provide alternatives to chemical-based methods, have given added impetus to the search for novel enzymes with unique and industrially significant traits. Thus, numerous organisms have been isolated from extreme environments. From the frosty A ntarctic ice fields to t he fiery v olcanic p ools, these o rganisms p ossess unique survival kits that allow them to survive under these extreme conditions. In most cases, adaptation to such extreme environments has not required completely new molecular machinery in fact many "extremophilic enzymes are similar to dieir mesophilic counterparts found in more hospitable environment. Sequence comparisons indicate that these enzymes are derived from a common... 

There are many existing and potential industrial applications of extremophilic enzymes (see Table 2), which take advantage of their capacity to thrive in harsh conditions, relative to their mesophilic (ie, function under moderate conditions) counterparts. For example, the detergent industry makes extensive use of alkaline-stable proteases, accounting for approximately 30% of global enzyme production (27). Enzymes from extremophiles have been used for bioremediation heavy metals and radionuclides from wastewaters (28), as well as for biodegrading hydrocarbons in polar soils (29). It is likely that extremophilic enzymes will find wide use in applications that strategically use their intrinsic robustness as biocatalysts. 

Enzymes for Extreme Conditions. The possibihty of using enzymes from extremophiles, which thrive in oil wells, hot temperatures, freezing conditions, etc, is being explored for the removal of environmental contaminants and survival at extreme temperatures (see Wastes, HAZARDOUS WASTE TREATlffiNT BlORETffiDIATION (SuPPLET NT)). 

To overcome this shortcoming, biologists turned to an enzyme that could survive the PCR hot cycle. They replaced the original heat-sensitive enzyme with DNA-polymerase from Thermus acqua-ticus, the Yellowstone extremophile. The new enzyme is unscathed... 

The structural integrity of enzymes in aqueous solution is often compromised by the addition of small quantities of water-miscible organic solvents. However, there are numerous examples, particularly using extremophiles, where enzymes have been successfully employed in organic solvent-aqueous mixtures.A good example is the savinase-catalysed kinetic resolution of an activated racemic lactam precursor to abacavir in 1 1 THF/water (Scheme 1.39). The organic solvent is beneficial as it retards the rate of the unselective background hydrolysis. 

Enzymes from extremophiles, such as thermozymes, have potential either as products themselves, or as catalysts, or they may be used as sources of ideas to modify mesophile-derived enzymes. Most of the thermozymes maintain their thermoresistant properties when expressed in a mesophilic organism such as... 

F. Niehaus, C. Bertoldo, M. Kahler, and G. Anthranikian, Extremophiles as a source of novel enzymes for industrial application, Appl. Microbiol. Biotechnol. 

The once-obscure field of exploring potential uses of bacteria and their enzyme systems that thrive in hot or boiling water (extremophiles)—from geysers and sea bed vents in tectonically active areas—is another instance of nature generating practically valuable resources. The use of hyperthermophilic enzymes to speed the fermentation of ethanol from starch is a case in point.33... 

Proteins from extremophilic organisms, particularly thermophiles, have been the subject of intensive research in recent years. This work has been the subject of numerous reviews (Jaenicke and Bohm, 1998 Russel and Taylor, 1995 Vogt and Argos, 1997 Gerday et al., 1997 Somero, 1995), and we will make no attempt at an in-depth summary. We will confine ourselves to briefly stating the major trends identified thus far. Explaining these trends becomes complicated because the many weak interactions that determine enzyme stability and activity have complex temperature dependencies (see Section II). And evolution injects considerable confusion beyond the laws of physical chemistry. 

PHENOMICS platform) and screen for potential uses in biotechnology. Table 31.11 lists different classes of extremophiles from which useful enzymes have been derived. Further information on extremophiles and their potential utility for biocatalysis can be found in the reviews by Van den Burg (2003) and Gomes and Steiner (2004).31 32... 

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