short communications
Methyltetrahydrofolate:corrinoid/iron sulfur protein methyltransferase from Clostridium thermoaceticum has been crystallized in two polymorphic forms and characterized by X-ray diffraction measurements. Form I displayed orthorhombic symmetry with a = 63.9, b = 53.8, c = 164.0 Å. Form II also displayed orthorhombic symmetry with a = 63.5, b = 87.1, c = 117.9 Å. Crystals of form I diffract to approximately. 3 Å resolution; those of form II diffract to approximately 2.7 Å.