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half-seriously...old-school method: - apart from the excellent suggestions by Juergen and Phil, you could experimentally determine the density of the crystals and calculate their protein content from that. This looks like a fun method to try: http://journals.iucr.org/j/issues/1999/05/00/wb0070/wb0070.pdf (some work, but would be an independent way to estimate the solvent content) Mark J van Raaij Lab 20B Dpto de Estructura de Macromoleculas Centro Nacional de Biotecnologia - CSIC c/Darwin 3 E-28049 Madrid, Spain tel. (+34) 91 585 4616 http://www.cnb.csic.es/~mjvanraaij On 21 Nov 2013, at 18:35, Meisam wrote: > Dear CCP4ers > > I have a data set that diffracts 1.96 Å. It scales in P21 Space group with 7% linear Rfactor. > The Mattew coefficient gives 10% probability for 3 molecules in the asymmetric unit, 53% for 4 molecules, and 36% for 5 molecules. > Molecular replacement just finds 3 molecules in the asymmetric unit. Running Phaser also gives a partial solution with 3 molecules. > When I refine just the back bone of the protein for the 3 molecules the Rfree/Rwork does not go better than 34% / 31%, and when I run the molecular replacement on the refined structure again, and I fix it as a model to search for another molecule, it still does not find it. > > I have attached a photo to show the density for the fourth molecule in the asymmetric unit. > > What is the solution to this? > > Thanks in advance for your help > > Meisam > <An Extra Molecule.png>