Abstract
Anomalous dispersion of X-ray diffraction from bovine trypsin has been measured at three wavelengths near the K-absorption edge of sulphur (λK = 5.02 Å) which are characteristic of sulphur in methionine and the cystine disulphide bridges. The feasibility of phasing by means of the dispersion analysis is demonstrated in two steps:
1. Scaling of the experimental data and calculation of the anomalous difference Patterson map, showing the correlation between sulphur atoms.
2. Using the measured dispersion to calculate phases based on the known sulphur sites of the refined trypsin model.
Although the resulting electron density map of 5 Å resolution is calculated from 600 unique reflections only, there is a reasonable agreement with the superimposed molecular model.
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