Purification, Stability, and Composition of Formyltetrahydrofolate Synthetase from Clostridium thermoaceticum

Formyltetrahydrofolate synthetase has been purified to near homogeneity from the thermophile, Clostridium thermoaceticum, as judged from sedimentation velocity, amino-terminal analysis, and electrophoresis. The enzyme is exceptionally stable at high temperatures, especially at pH 7.0. Ammonium or potassium ions enhance its stability between pH 6 to 9. These ions are not required for activity, however. There is little or no carbohydrate or lipid present in the enzyme. The partial specific volume calculated from the amino acid composition is 0.747 cc per g. The thermostable formyltetrahydrofolate synthetase isolated from C. thermoaceticum is somewhat more hydrophobic than the similar enzyme isolated from two mesophilic Clostridia. Although the difference in hydrophobicity is small, it may explain the higher thermal stability of the enzyme from C. thermoaceticum.