Tandem genetic duplications in Salmonella typhimurium: amplification of the histidine operon.

Bovine pancreatic phospholipase A₂ (M_r = 14,000) has been crystallized and its three-dimensional structure determined by X-ray diffraction analysis to a resolution of 2.4 Å. Three heavy-atom derivatives were used in the phase calculations with inclusion of the anomalous dispersion differences. The resulting electron density map allowed an easy and unambiguous tracing of the peptide chain. Two of the seven disulfide connections appeared to be different from what was suggested by the earlier chemical and structural work. The bovine phospholipase A₂ structure contains about 50% α-helix and 10% β-structure. The bovine enzyme structure was found to deviate substantially from the previously published porcine prophospholipase structure.