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Re: request for additional token

herbert_bernstein (yaya@aip.org)
Fri, 27 Oct 95 18:26:41 EDT 

Here, for those who don't have it handy, is the 1992 PDB commentary
on Z, which shows, I think, how close to the existing mmCIF
Z value definition it is:

"Confusion over the value to use for Z (number of molecules per cell)
arises because of different conceptions of the meaning of 'molecule'.
We have adopted the (crystallographic) convention that Z should equal
the number of times the same polymeric chain is contained in the cell.
In case of different numbers of chains per cell this will be explained
in the REMARK section and Z will denote the number of the more
populous species per cell."

That being said, it would seem the definition of _cell.formula_units_Z
would work with the addition of the following:

For macromolecular structures, the value of _cell.formula_units_Z
is the number of occurances of the entity defined by _entity_poly_seq
in the cell.  For heterogeneous combinations of polymers for which
the populations of distinct polymeric entities with a cell differs,
the value for the most populous ones will be used.

This is not a critical issue, but it would seem helpful to users
of future multidisciplinary data base searches to use the same name
for a common concept where possible.