Partial Characterization of Fumarase from an Extreme Thermophilic Bacterium Isolated in Indiana

Fumarase (L-malate hydro-lyase E.C. 4.2.1.2) was partially purified from a gram negative, non-spore forming, extreme thermophilic bacterium isolated from a steam chamber on the Indiana University Campus at Bloomington, Indiana. This isolate is very similar to the Thermus X-l isolate previously reported by Ramaley and Hixson and is designated as the Thermus K-l isolate. The K-l fumarase has an apparent molecular weight of 170,000, a broad bell shaped pH optimum between pH 7.5 and pH 11, with L-malate as a substrate and an apparent Michaelis constant (Km) for L-malate of 3.3 ± 0.4 millimolar. The K-l fumarase is fully heat stable for 30 minutes at temperatures up to 85° Centigrade. An Arrhenius plot of the enzyme catalyzed reaction showed an inflection (critical point) at 70° Centigrade with an apparent activation energy of 12,000 calories below 70° Centigrade.