Difference structure-factor normalization for heavy-atom or anomalous-scattering substructure determinations

Abstract

Procedures are described for normalizing structure-factor difference magnitudes, |Δ|F||SIR= ||FDer| − |FNat|| ≤ |FHeavy| or |Δ|F||SAS= ||F+h| − |F−h|| ≤ 2|F′′|, to prepare data for probabilistic direct methods phasing to determine heavy-atom or anomalous-scattering substructures in SIR (single-derivative isomorphous replacement) or SAS (single-wavelength anomalous scattering) cases. Applications of the procedures in several recent determinations of multi-selenium substructures in selenomethionyl proteinsviaSnBdirect-methods phasing are briefly summarized.