ABSTRACT
Enzymatic preparations of two isoforms of succinate dehydrogenase (SDG) with specific activity of 22.00 E/mg of protein were obtained from the colorless sulfur bacterium Sphaerotilus natans D-507 cultured organotrophically. Both SDG forms were shown to be heteromers with subunit molecular masses of 70.8, 35.0, 31.8, and 16.2 kDa. The K(m) values for the first and the second forms of SDG were evaluated as 0.615 and 0.531 mM, respectively, with an optimal pH value of 7.2. It was found that the Cl- ion has an activating effect on the SDG activity that can be explained by the specific chemical modification of the enzyme molecule. The results suggest that the isolated enzyme forms are included in different multienzyme complexes, which provide the functioning of the tricarboxylic acid cycle, and SDG preparations can be used for the investigation of other enzyme systems or in vitro modeling of supramolecular cellular structures.
