Hi Jose, It is quite difficult to crystallize DDM. The main problem is to estimate detergent concentration in the final sample. One method requires the use of chromatographic workstation coupled to a light scattering detector and refraction index measurement unit. In this case you can know if there is an excess detergent (particularly likely to be the case if you are using a low CMC detergent like DDM and if you have been concentrating your sample on a membrane with a cutoff smaller than the empty micelles). This is more involved and requires a specialized equipment. But you can detect both your protein and your excess detergent (if there is). Also to test you crystals, you may want to see if you can access a fluorescence microscope. If your protein contains tryptophan (and you have the correct wavelength) then you protein crystals should glow. Your detergent crystals should not. Those microscopes are getting more and more popular so maybe you have one next by. It is very convenient.
Hope this helps Pascal Egea, PhD University of California Los Angeles Department of Biological Chemistry
