Electron Density Map File

The electron density map file in X-PLOR contains information about the crystal unit cell, indexing of the map, and the actual electron density map. Because helical structure does not have a crystal unit cell, the unit cell parameters in the map file of fiber_refin-map-statment are replace by the dimensions of the electron density map:

$a$ = the length (Å) of the map in x direction. 

$b$ = 		 the length (Å) of the map in y direction. 

$c$ = 		 the length (Å) of the map in z direction. 

$\alpha$ = 		 $90.0^o$ 

$\beta$ = 		 $90.0^o$ 

$\gamma$ = 		 $90.0^o$

The map file can be read by a modified version of MAPPAGE to provide a ``DSN6'' file for FRODO. This modified version is included in XPLOR distribution package from Brünger. The grid size of the map is determined by the GRID parameter.