S-adenosylmethionine synthetase from Escherichia coli. Crystallization and preliminary X-ray diffraction studies.

S-Adenosylmethionine synthetase from Escherichia coli can be crystallized by the method of vapor diffusion using ammonium sulfate as the precipitant. Two of several crystal forms of the tetrameric (Mr = 180,000) enzyme have been examined by x-ray diffraction methods. One form, a hexagonal bipyramid, develops when Mg2+ and PPi are added to the protein solution. The space group is P62(22) or P64(22) with a = b = 128.8 A, c = 140.0 A, and one subunit in the asymmetric unit. The other, a regular octrahedron, forms with the addition of 5% (v/v) 2-methyl-2,4-pentanediol. It is of space group P41(2)1(2) or P4(3)2(1)2, with a = b = 121.8 A, c = 172.6 A, and two subunits in the asymmetric unit.