Crystallization, characterization and preliminary crystallographic studies of carbamate kinase of Streptococcus faecium.

Crystals of carbamate kinase (E.C.2.7.2.2) suitable for high resolution studies have been obtained, using the hanging drop vapour diffusion technique, with polyethylene glycol 8000 and NaCl as precipitants at pH 6.5 and a temperature of 4 degrees C. Crystals of about 0.3 mm x 0.2 mm x 0.2 mm in size diffract to at least 3.2 A resolution and are stable to X-radiation for more than ten hours. The space group is P2(1)2(1)2(1), with unit cell dimensions a = 84.5 A, b = 99.6 A, c = 173.3 A. Density packing considerations are consistent with the presence of four to five monomers (M(r) of the monomer = 33,000) in the asymmetric unit, two dimers or even a tetramer being favoured by the results of cross-linking experiments of the enzyme in solution.