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 degrees C. 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 degrees C, The enzyme was also resistant to chemical denaturants; 50% of the initial specific activity was detected in assay mixtures containing 0.8 RI 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. (C) 1998 Academic Press.