Thermophilic enzymes, properties

The lower stability of psychrophilic and mesophilic enzymes relative to their counterparts from thermophiles is likely to be the product of genetic drift, or have occurred during adaptation of other properties... 

Lipases are the most common enzymes used in non conventional media like organic solvents and supercritical carbon dioxide. Lipases usually hydrolyse fats into fatty acids and glycerol. The special property of lipases is their ability to act at the interface between water and oil. In these experiments lipase (EC 3.1.1.34) from Rhizopus arrhizus (Boehringer Mannheim) was used to investigate the effects of lipase under hydrostatic pressure. The analysed reaction was the hydrolysis of p-Nitrophenyllaureate at different concentrations at 35 °C. The dependance of the kinetic constants between 1 bar and 3000 bar is presented in table 2. Like the thermophilic GDH at 1000 bar lipase is activated under pressure as well. The initial reaction rate increases by a factor of 1.5 at 1000 bar compared to the initial reaction rate at ambient... 

Alanine racemases are homodimeric enzymes of an apparent molecular mass of 76kDa, containing two molecules of PLP as co-enzyme [61] the known enzymes from different sources are highly homologous. With regard to the kinetic properties, the values for D- and L-Ala determined at 30 °C for the Pseudomonas fiuorescens alanine racemase are -12 and 19mM, respectively and the Vnm values for racemization are -1200 and 2200 units/mg protein, respectively. The thermophilic alanine racemase from B. stearothermophilus is quite stable to heat treatment (up to 75 °C for 1 h) while the mesophilic one from B. subtilis is stable up to 55 °C under the same conditions. 

Most tungstoenzymes isolated so far have been from obhgate anaerobes that are also thermophilic to a greater or lesser extent. Moreover, the enzymes have similar catalytic properties. They all catalyze a redox reaction involving conversions at the level of carboxyhc acids and aldehydes (with the exception of AH). However, their physiological roles are distinctly different. 

Enzymes isolated from extremely thermophilic archaea and characterized with respect to their thermophilic properties ... 

Although a considerable number of extracellular and intracellular proteins have been isolated and described from thermophilic archaea, few detailed studies concerning the structure and thermophilic properties of the respective proteins are available. Of the approximately 40 different enzymes isolated from the extremely thermophilic archaea and characterized with respect to basic thermophilic properties (Table 1), only eight have been analyzed with respect to their primary structure, mostly using the nucleotide sequence of the coding genes, and in no case could the three-dimensional structure of the proteins be resolved. 

A DNA-dependent ATPase activity was found associated with the purified enzyme [77]. In contrast, an ATP-independent relaxation activity detected in partially purified fractions of reverse gyrase [74] was absent from completely purified fractions and probably corresponds to a distinct DNA topoisomerase (see below). A reverse gyrase with similar structure and properties was purified later by Slezarev[78] from another extremely thermophilic archaebacterium, Desulfurococcus amylolyticus[7S],... 

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