Enzymes extremozymes

Extremozymes—enzymes that can tolerate relatively harsh conditions, suggested as catalysts for complex organic synthesis of fine chemicals and pharmaceuticals (Govardhan and Margolin, 1995). 

Extremozymes, enzymes from thermophilic bacteria, have become important in synthetic chemistry. 

The mixtures of extremozymes produced by the expression process are then tested to see if they have catalytic activity for the industrial processes of interest. If a given mixture shows catalytic activity, it is then usually subjected to random DNA mutagenesis or molecule breeding to see whether random evolution of the enzymes will lead to improved activities. 

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... 

Enzymes that function under extreme conditions (extremozymes) and in organic media... 

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). 

Because extremozymes function under conditions that are so far removed from normal, research into their behavior is intense. One of the research goals is to develop ways to use enzyme... 

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... 

Thermophilic bacteria, growing in hot springs like these at Yellowstone National Park, produce heat-stable enzymes called extremozymes that have proven useful for a variety of chemical processes. 

The preference of many NADH-dependent enzymes for either the re or si face of their respective substrates is known. This knowledge has allowed some of these enzymes to become exceptionally useful stereoselective reagents for synthesis. One of the most widely used is yeast alcohol dehydrogenase. Others that have become important are enzymes from thermophilic bacteria (bacteria that grow at elevated temperatures). Use of heat-stable enzymes (called extremozymes) allows reactions to be completed faster due to the rate-enhancing factor of elevated temp>erature (over 100 °C in some cases), although greater enantioselectivity is achieved at lower temperatures. 

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