Solve the phasing problem at home with Cr-radiation
The single-wavelength anomalous dispersion method (SAD) is frequently used to solve protein structures from synchrotron data by taking advantage of the tunable wavelength to collect heavy atom derivatives near the metal's absorption edge. For methionine-containing proteins, selenomethionine derivates may be prepared to take advantage of the anomalous Se signal.
However, some proteins will not crystallize as SeMet derivatives, and not all proteins contain methionine. Sulfur, on the other hand, is present in almost all proteins in cysteine residues. The process of structure solution is greatly simplified if SeMet substitution or heavy-atom soaks are not necessary.
The structure of crambin was solved in 1981 using the resolved atom S-SAD method and Cu Kα radiation and a number of other proteins have been solved using Cu or synchrotron radiation tuned to near-Cu wavelengths.