Temperature 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... 

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... 

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)). 

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. 

A number of smaller enzyme-producing companies focus on thermophilic micro-organisms (and other extremophiles) to identify and produce new types of thermostable enzymes Unitika, Pacific Enzymes, Genis, Diversa (formerly Recombinant BioCatalysis), and others. One extremozyme that has already found commercial application is the heat-stable DNA polymerase from Thermus aquaticus (Taq-polymerase) that gave rise to the polymerase chain reaction (PCR). Using PCR, nucleic acids or segments of DNA can by amplified in vitro without having to replace the enzyme after each amplification cycle when the DNA template is denatured by heat. A number of new hyperthermophilic enzymes with temperature optima between 75 and 118°C have been described in the past few years [81], such as... 

The enzymes produced by these extremophiles, known as extremozymes, can function under extreme conditions. An illustrative list along with an indication of the extreme environments in which they can function is included in Table 20.1 (sources Kushner, 1978 Jones et al., 1983 Huber et al., 1989 Li et al., 1993 Davail et al., 1994 Adams et al., 1995). Enzymes extracted from these microorganisms have been tested for a variety of reactions and optimum temperatures have been found. Examples are enzymes from Pyrococcus furiosus for a- and p glucosidase, a-amylase, protease, and hydrogenase activities (Bryant and Adams, 1989 Costantino et al., 1990 Blumentals et al., 1990 Kegen et al., 1993 Laderman et al., 1993). 

Most of the enzymes used to date are obtained from mesophilic organisms and, thus, their limited stability to temperature, pH, or ionic strength. Ex-tremophiles are organisms that have evolved to exist in a variety of extreme environments. Table 3 lists the range of habitats where extremophiles have been found and some of the identified extremozymes. Adaptation to extreme conditions means that these enzymes have the same order of magnitude of activity and stability but at different temperatures, ionic... 

The reaction temperature is around room temperature, although some enzymes from extremophiles, microorganisms from extreme environmental conditions, can react very effectively at temperatures up to 120°C and down to -50°C. Sometimes, enantioselectivity can be improved by a decrease or increase in the reaction temperature. 

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