Characterization of the malate dehydrogenase from Thermoleophilum album NM

Malate dehydrogenase (MDH; EC 1.1.1.37) was characterized from Thermoleophilum album NM, a gram-negative aerobic bacterium obligate for thermophily and n-alkane substrates. The enzyme was purified by affinity chromatography and electroelution. The MDH had a mol.wt. of 61,000 and consisted of two subunits, each with a mol.wt. of 32,500. T. album NM MDH migrated further on nondenaturing polyacrylamide gels than did other MDHs. The MDH was active from 30°–95° C with optimum activity occurring at 60° C and pH 7.5. Kinetic data were determined at 60° C and pH 7.5. The Km values for malate and NAD were 1.41 mM and 0.26 mM, respectively. The Km for reduction of oxalacetate was 5.43 mM and 0.31 mM for NADH. The amino acid composition of T. album NM MDH differed in the amounts of Arg, Lys, Gly, Pro and His from the MDHs of other thermophilic and mesophilic organism. The N-terminal amino acid sequence had no appreciable homology with MDHs of other species.