| Enzymes from extremophilic microorganisms are of great interest to the biotechnology industry due to their activity and stability under extreme conditions. One of the most important and oldest groups of industrial enzymes is α-amylases, which catalyze the hydrolysis of internal linkages in starch to produce smaller sugars. The objective of this research was to evaluate the industrial potential of α-amylases from a hyperthermophile, isolated from a hydrothermal vent in the Atlantic Ocean, as well as from an alkaliphile, isolated from a soda lake in Tanzania.; The method used to produce an α-amylase from the hyperthermophile involved cloning and expression of the enzyme-specific gene in the mesophilic host Escherichia coli, whereas the production of an α-amylase from the alkaliphile entailed isolation directly from the natural host. The α-amylases exhibited biochemical characteristics typical to the environment from which the organisms were isolated. The recombinant α-amylase from the hyperthermophile displayed optimal activity at 90°C and pH 5.5, in the absence of exogenous calcium. It was stable at 90°C for up to 2 hours and thermal stability was further enhanced by the presence of calcium and starch. The enzyme was active in the presence of various cations, but was strongly inhibited by the chelator EDTA and copper. The extraordinarily high specific activity (7400 U/mg) exceeds that which has previously been reported for hyperthermophilic α-amylases. These properties render it very attractive as a potential biocatalyst in the starch process industry.; The activity profile of the wild-type α-amylase from the alkaliphile displayed strong synergistic effects of temperature and pH on activity. The pH optimum for activity varied with the temperature, below 40°C maximum activity was observed at pH 10, whereas above 40°C the pH optimum shifted to 7. The enzyme was thermolabile and displayed very low specific activity (19 U/mg). Furthermore, it was inhibited by the presence of various cations, including calcium, but was found to be resistant to the chelating agent EDTA. A potential industrial use of this α-amylase could be as an additive to detergents used in cold-washing; however, due to its very low specific activity, it cannot compete with other available alkaliphilic α-amylases. |
