IUPAC Labeling Conventions

The IUPAC has defined the labels for certain atoms in a couple amino acids in terms of an artificial chirality. These residue are valine and leucine. The file iupacgeo.dat contains the definitions of these ``chiral centers'' so that an inversion of the side chain of one of these residues can be monitored. If a valine or leucine beta carbon inverts the atom labels should be switched to keep the PDB people happy. This library also contains the definition of the appropriate ``chi'' angles which the IUPAC uses to define the atom labels in ASP, GLU, PHE, and TYR. If the ``chi'' angle is greater than 90 degrees for one of these amino acids the labels should be exchanged. Since these restraints were designed to identify IUPAC convention matching they do not reflect the proper standard values. These torsion angles cannot be used in refinement.

Wed Jul 5 13:21:03 PDT 2000