Purification and characterization of a thermostable class II fumarase from Thermus thermophilus

A thermostable fumarase was purified from a strain of Thermus thermophilus isolated from a Japanese hot spring. The maximum specific activity of the purified enzyme was 1740 units/mg at pH 8.0 and 85 degreesC. The enzyme was composed of four identical subunits with a molecular weight of 46,000 and displayed other enzymatic characteristics which are common to the class II fumarases. The thermal stability of the purified enzyme was remarkable, with over 80% of the activity remaining after a 24-h incubation at 90 degreesC. The enzyme was also resistant to chemical denaturants; 50% of the initial specific activity was detected in assay mixtures containing 0.8 M guanidine hydrochloride. The purified enzyme shared an extremely high sequence homology with Thermus aquaticus fumarase and Bacillus subtilis fumarase in the first 43 amino acid residues.