Crystallization and preliminary X-ray diffraction studies of E. coli porphobilinogen synthase and its heavy-atom derivatives.

Porphobilinogen synthase (PBGS) catalyzes the condensation of two identical substrate molecules, 5-aminolevulinic acid (ALA), in an asymmetric manner to form porphobilinogen. E. coli PBGS is an homooctameric enzyme. The number of active sites is not clear, but each subunit binds one ZnII ion and one MgII ion. Diffraction-quality crystals of native E. coli PBGS have been obtained, and unit-cell dimensions (a = 130.8, c = 144.0 A) are reported. These crystals diffract to about 3.0 A resolution.