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request for additional token

Frances Bernstein (bernstei@fcb.pdb.bnl.gov)
Thu, 26 Oct 1995 14:32:10 -0400


The PDB has a field on CRYST1 records that is called Z but it
is not the same as the crystallographic Z.  Here is the definition
from the PDB format description:

The Z-value is the number of polymeric chains in a unit cell. In the
case of heteropolymers, Z is the number of occurrences of the most
populous chain.

I do not think there is a need to have a discussion about the meaning
or the usefulness of this parameter; it has been present in PDB entries
as long as the present format has existed.  What would be appreciated
would be the addition of a field in the mmCIF dictionary that would
hold this quantity and would facilitate the translation of PDB to mmCIF
and vice versa.

                                     Frances C. Bernstein