Purification and Catalytic Properties of “Thermostable” Fumarase from Bacillus Stearothermophilus NU-10 and Thermus X-1

Fumarase (L-malate hydro-lysase E.C.4.2.1.2) was purified from the thermophilic bacteria Bacillus stearothermophilus NU-10 (optimum growth temperature 62-63 degrees C) and Thermus X-1 (optimum growth temperature 70 degrees C). The furmarase from Thermus X-1 is slightly more thermostable and has an "optimum" catalytic reaction temperature of 83 degrees C as compared to 81 degrees C for the B. stearothermophilus enzyme. Increased thermostability of these fumarases permitted an examination of the properties of the enzyme catalyzed reaction at temperatures higher than had previously been possible with the furmarases from mesophilic bacteria or higher plant and animal sources. Beyong the observed thermostability of the thermophilic fumarases, the catalytic properties of thermophilic fumarases were very similar to those observed with bacterial fumarase or the well characterized pig heart fumarase (effect of temperature on substrate affinities, pH optimum, substrate inhibition by fumarate, and Haldane relationship). These similarities suggest that thermophilic enzymes may be useful in the general study of enzyme reaction mechanisms.