Chapter 12.2 Locating heavy-atom sites

Crystallography of biological macromolecules

Second Online Edition (2012)

Part 12. Isomorphous replacement

  1. M. T. Stubbs1,
  2. R. Huber2

Published Online: 14 APR 2012

DOI: 10.1107/97809553602060000838

International Tables for Crystallography

International Tables for Crystallography

How to Cite

Stubbs, M. T. and Huber, R. 2012. Locating heavy-atom sites. International Tables for Crystallography. F:12:12.2:327–332.

Author Information

  1. 1

    Institut für Pharmazeutische Chemie der Philipps-Universität Marburg, Marbacher Weg 6, D-35032 Marburg, Germany

  2. 2

    Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany

Publication History

  1. Published Online: 14 APR 2012


In order to obtain phase information from isomorphous replacement (or from anomalous dispersion), it is necessary to locate the atomic positions of the heavy-atom (or anomalous) scatterers. The topics covered in this chapter include: the origin of the phase problem; the Patterson function; difference Fourier maps; treatment of errors; automated search procedures; and special complications such as lack of isomorphism, space-group problems and high levels of substitution.


  • Fourier maps;
  • Patterson functions;
  • difference Fourier maps;
  • heavy-atom location;
  • isomorphism;
  • isomorphous replacement;
  • lack of isomorphism;
  • noncrystallographic symmetry;
  • phase problem