Hi Zhen -was concentration higher in old run? Might be monomer-dimer equilibrium, for recent paper, see Benfield et al. (JBC, in press) -we have a miniDAWN with a 'low-high-medium' setting in the back of the setting. Inadvertently changing the setting scales the MW values up and down. Have you run a BSA standard, to insure system is OK? -Amir ________________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] On Behalf Of zhen zhang [zz2...@columbia.edu] Sent: Thursday, April 21, 2011 5:32 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Puzzle with MALS
Dear All, I am having a consistency issue processing my SEC-MALS data. The sample is a 80KD protein which may form a dimer. The experiment I run a year ago shows a major peak at 11.4 ml (GE S200 column), which is calcuated to have a MW of 144kD. There is a minor peak at 10.0 ml. In an effort to make nice looking pictures, I rerun the experiement using the same setup (column, buffer, protein, speed) and again the major peak is at 11.4 ml but it is calcuated to have a MW of 80KD. I rerun the sample multiple times with the same result. I tried to reprocess the old data and the calcuated MW is still 144KD. I am puzzled about what I have done wrong and which data I should trust. Well, I am inclined to trust the later experiment because I took extra caution and had multiple data sets. However, I should be able to reprocess the old data to have a MW close to 80KD if I can find out what is wrong and correct the mistake, which I have not been able to. Any suggestions? Zhen Zhang
