The 6 Å structure and biological activity of crystals of Δ5-3-ketosteroid isomerase

The crystal structure(P2~ 2.:2i 2 :protomers/asymmetric unit) of the dimeric (••.;) phospholipase A, from Crotalus atrox has been dete:rm.inedto 2.5 A resolution by MIR augmented by real space direct methods.A skeletal model was fit to the electron density and the stereochemistry of the backbone was idealized.The dimeric molecule forms a smooth oblate ellipsoid composed of two covalently identical subunits related by a local dyad axis which is nearly 1 exact'.Much of the architecture of the individual nrotomers resembles the structure of the homologous mono~eric bovine enzsille [Dijkstra, B.\1., et