Location of heavy-atom sites

Matthews, B. W.

doi:10.1107/97809553602060000685

International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

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International Tables for Crystallography (2006). Vol. F. ch. 14.1, p. 297 | 1 | 2 |

Section 14.1.10. Location of heavy-atom sites

B. W. Matthews^a ^*

^aInstitute of Molecular Biology, Howard Hughes Medical Institute and Department of Physics, University of Oregon, Eugene, OR 97403, USA
Correspondence e-mail: brian@uoxray.uoregon.edu

14.1.10. Location of heavy-atom sites

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During the development of protein crystallography, it was understood that heavy-atom sites might be located from difference Patterson functions, but there was substantial debate as to the type of function that was preferable (Perutz, 1956).

Blow (1958), and also Rossmann (1960), advocated a Patterson function with amplitudes $[(F_{PH} - F_{P})^{2}]$ . It relies on the admittedly crude assumption that the desired scattering amplitude of the heavy atoms, $[|F_{H}|]$ , can be approximated by $[|F_{H}| \simeq |F_{PH} - F_{P}|. \eqno(14.1.10.1)]$ The approximation does have one very helpful characteristic, namely, that it tends to be most accurate when $[|F_{PH} - F_{P}|]$ is large, i.e. when $[F_{H}]$ is parallel or antiparallel to $[F_{P}]$ (cf. Fig. 14.1.4.1). Thus, the numerically largest coefficients in the Patterson function tend to represent $[|F_{H}|^{2}]$ correctly. Given a well behaved isomorphous heavy-atom derivative, and accurately measured data, experience has shown that a map with coefficients $[(F_{PH} - F_{P})^{2}]$ can give an excellent representation of the desired heavy-atom–heavy-atom vector peaks.

References

Blow, D. M. (1958). The structure of haemoglobin. VII. Determination of phase angles in the non-centrosymmetric [100] zone. Proc. R. Soc. London Ser. A, 247, 302–336.Google Scholar

Perutz, M. F. (1956). Isomorphous replacement and phase determination in non-centrosymmetric space groups. Acta Cryst. 9, 867–873.Google Scholar

Rossmann, M. G. (1960). The accurate determination of the position and shape of heavy-atom replacement groups in proteins. Acta Cryst. 13, 221–226.Google Scholar

International Tables for Crystallography (2006). Vol. F. ch. 14.1, p. 297