Chapter 12.2 Locating heavy‐atom sites

Crystallography of biological macromolecules

First Online Edition (2006)

Part 12. Isomorphous replacement

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

Published Online: 1 JAN 2006

DOI: 10.1107/97809553602060000680

International Tables for Crystallography

International Tables for Crystallography

How to Cite

Stubbs, M. T. and Huber, R. 2006. Locating heavy‐atom sites. International Tables for Crystallography. F:12:12.2:256–262.

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: 1 JAN 2006



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