As mentioned lots of reasons for this.
a. Poor crystal
b. Poor mount of the crystal
c. Poor equipment or non-working equipment
d. Poor maintenance of good equipment
e. Improper cryoprotection
f. Vibration or movement of goniometer, goniometer head, mounting pin, mounting
loop, magnet, etc
g. Temperature fluctuation of the environment during the data collection
h. Not enough exposure time or poor signal to noise (improper experimental
design)
i. Improper data processing (too many things to mention here)
j. etc.
k. et al.
Jim
________________________________
From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of hamid khan
[hamid...@yahoo.com]
Sent: Friday, March 29, 2013 8:19 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] High Rmerge and I/sigma values....?
Dear CCP4BB Members,
I am interested in your expert comments/opinions about two values of a protein
crystal diffraction data. Basically I am new to this field and do not have much
idea about diffraction data interpretation and crystallography software’s use.
1) What could be the possible reasons for a high Rmerge value, say like
0.185?
2) Value 6.2 for average I/sigma(I) for higher shell means that the
resolution of the diffraction data is much higher than actually measured, what
could be the possible reasons for this?
For your ease I would like to past the table here;
Values in parentheses are for the last resolution shell
Space group P2221
Unit-cell parameters (A°)
a 58.08
b 101.32
c 103.47
Molecules in ASU 1
Resolution range 38.63 - 2.50 (2.59 - 2.50)
Total number of reflections 228902
Number of unique reflections 21600
Completeness (%) 99.1 (98.0)
Rmerge 0.185 (0.373)
Reduced χ2 0.94 (1.01)
Average I/σ(I) 9.8 (6.2)
Thanks for the tips..,
Hamid Khan
