 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 4]](yt5011fig4mag.jpg)
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Figure 4
Detection and estimation of the twinning fraction in SAG506-01 crystal 1 (left) and crystal 2 (right) both reduced in the Patterson group P4/mmm. (a) The N(Z) plot of acentric reflections of SAG506-01 shows that the observed values (blue lines) are lower than the theoretical values (red lines) and sigmoidal, indicating the presence of twinning. (b) Estimate of the twinning fraction using the Britton plot (Britton, 1972  ). The percentage of negative intensities after detwinning is plotted as a function of the assumed value of the twin fraction (α). Overestimating the value of α results in an increase in the negative intensities. The true value of α can then be estimated from this increase. The twin fraction was estimated from where the dotted line intersects the x axis and was estimated to be 0.442 for crystal 1 (left) and 0.445 for crystal 2 (right). (c) Estimate of the twinning fraction using the H plot (Yeates, 1988). The cumulative fractional intensity difference of acentric twin-related intensities, H = |I1 − I2|/(I1 + I2), is plotted as a function of H. The twin fraction is estimated from the initial slope of this intensity distribution (dotted line) and was estimated to be 0.478 for crystal 1 (left) and 0.477 for crystal 2 (right). The cumulative intensity distribution, Britton and H plots were all calculated using phenix.xtriage as implemented in PHENIX (Adams et al., 2002). |
![[Figure 4]](yt5011fig4.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
