Physical properties of formyltetrahydrofolate synthetase from Clostridium thermoaceticum.

The hydrodynamic parameters of the thermostable formyltetrahydrofolate synthetase from Clostridium thermoaceticum have been measured in the ultracentrifuge at 20”. &J,~ = 9.86 f 0.20 S;vzo = 0.752 f 0.011 cc per g; and molecular weight = 244,000 f 9,000. Calculations based on these parameters give a frictional ratio, f/f0 = 1.27 f 0.11, and a Stokes radius of 53.0 f 4.8 A. The sedimentation constant from sucrose density gradient centrifugation is 9.9 f 0.4 S, and the Stokes radius of the enzyme from chromatography on a calibrated Sephadex G-200 column is 55.1 A. There are four subunits per 244,000 molecular weight. The fluorescence emission spectrum indicates that the tryptophans in the enzyme are in a moderately hydrophobic environment at 20”. The hydrophobicity possibly increases when the enzyme is heated to 56”, which is near the temperature optimum of the enzyme. The data show that the enzyme is not a random coil at 20 or 56”.