A reciprocal-space method for calculating a molecular envelope using the algorithm of B.C. Wang

A method is described to determine the molecular envelope from an isomorphous replacement phased electron density map using the reciprocal-space equivalent of B. C. Wang's algorithm [Wang (1985). In Methods in Enzymology, Vol. 115: Diffraction Methods for Biological Macromolecules, edited by H. Wyckoff, C. H. W. Hirs & S. N. Timasheff. New York: Academic Press.]. In the case of chloramphenicol acetyl transferase the computation time was reduced from 35 h (using the real-space algorithm) to 40 min.