Why use chromium radiation in the home lab?
Chromium radiation (2.29 Å) doubles the available anomalous signal from elements such as S, Ca and Se as compared to the signal available with copper radiation (1.54 Å). This enhanced signal has allowed the structures of thaumatin and trypsin to solved using that signal with relatively small data sets, 45° and 180°, respectively. Work is currently progressing on the structure of glucose isomerase using only Cr radiation enhanced data.
The chromium radiation enhanced anomalous signal may also be used to augment SIRAS data that is insufficient to phase the data alone. In effect, using chromium radiation adds a second heavy atom, which concomitantly reduces the phase error and in turn yields more easily interpretable electron density maps. This procedure was essential to phase the structures of two proprietary proteins in our Home Lab.
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| Table. 1 Increase in f" for sulfur, calcium and selenium with chromium radiation versus copper radiation. |
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Table 2. Experimental improvement in <ΔF>/<F> thaumatin, trypsin and glucose isomerase for chromium radiation versus copper radiation. |
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Who should use Chromium radiation?
Investigators who wish to increase the throughput of de novo structure solution in their home laboratory. This would include investigators involved in the Structural Genomics Initiative who wish to solve structures between synchrotron trips.
How do you use Chromium radiation?
- Read the Rigaku Journal article Practical Aspects of SAS Structure Determination Using Chromium X-rays
- See also: Solving the structure of the bubble protein using the anomalous sulfur signal from single-crystal in-house Cu K diffraction data only by J. G. Olsen, C. Flensburg, O. Olsen, G. Bricogne and A. Henriksen, Acta Cryst. (2004). D60, 250-255. [Read the abstract]