With Izit or other dyes, you might wish to do a positive control with bona fide protein crystals and a negative control with bona fide salt crystals. _____
From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Matthew Bratkowski Sent: Tuesday, November 16, 2010 7:58 PM To: [email protected] Subject: Re: [ccp4bb] how to optimize small rod-shaped crystals I like using Izit dye from Hampton (http://hamptonresearch.com/product_detail.aspx?cid=4 <http://hamptonresearch.com/product_detail.aspx?cid=4&sid=41&pid=33> &sid=41&pid=33) to check if crystals are protein or salt. If the crystals are protein, the dye should absorb rather readily into the crystals and turn them blue, while the rest of the drop will eventually turn clear. Quite likely, excess dye will also crystallize out as well. Salt crystals will not soak in the dye, and the rest of the drop may remain blue for several days. Using Izit is easy and saves a lot of time. In my experience, I have gotten a lot of false positives from phosphate crystallization conditions, so you want to be sure that the crystals are not salt before you waste any time on optimizing them. Matt
