Preliminary X-ray crystallographic analysis of thermolysin in the presence of 4 M NaCl

The activity of thermolysin (EC 3.4.24.27) is greatly enhanced by high concentrations of neutral salts. For instance, 4 M NaCl enhances the activity 13-15-fold [Holmquist & Vallée (1976), Biochemistry, 15, 101-107; Inouye (1992), J. Biochem. (Tokyo), 112, 335-340]. To clarify the structural basis of the activation of thermolysin by high concentrations of NaCl, we have developed a new method to introduce 4 M NaCl into the P6₁22 crystal of thermolysin originally grown without NaCl. The crystal obtained by this method diffracted X-rays to 2.43 Å. No unit-cell parameter change was observed except the length of the c axis, which was elongated by 9.6% by the introduction of 4 M NaCl.