STRUCTURE OF CRYSTAL FORM IX OF BOVINE PANCREATIC RIBONUCLEASE-A

The X-ray structure of crystal form IX of bovine pancreatic ribonuclea se A (space group P2(1)2(1)2(1)) is reported at 1.6 Angstrom resolutio n. The structure was refined to an R factor of 15.0% and includes coor dinates for two sulfate ions, four methanol molecules and 82 waters. T he structure could be superimposed on the highest resolution crystal s tructure of bovine pancreatic ribonuclease available (in space group P 2(1)) with an r.m.s. difference in main-chain atomic positions of 0.51 Angstrom. Most of the larger differences between the two structures c ould be related to crystal lattice contacts. Superposition of the new structure with eight other structures of ribonuclease in six crystal f orms resulted in an r.m.s. deviation from the average structure of 0.4 3 Angstrom for all main-chain atoms. This similarity among structures exists in spite of the fact that all nine molecules are in different c rystal environments.