If one tries to use a dye to determine if crystals are protein or salt, then I recommend that they use both a positive and a negative control. So have some handy salt or sugar crystals ready along with some known protein crystals to use as controls.
Jim ________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Ganesh Natrajan [ganesh.natra...@ibs.fr] Sent: Monday, February 11, 2013 3:37 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] protein crystals or salt crystals Dear Amro, What you could try is this. Make a solution of 0.5 % (w/v) commassie brilliant blue in 10% (v/v) ethanol in water. Pipet 1 ul of this into your drop and close the cover slip. If the crystals are protein, they should turn blue after some time (typically 30 mins). Salt crystals will not turn blue as they are not stained by commassie. You could also try using Hampton's Izit crystal dye for this, but the problem I have faced with it is that the izit itself crystallizes (gives lovely blue crystals) under certain buffer conditions. cheers Ganesh Hallo my colleagues. i hope every one doing ok . i did screening since two weeks . i noticed today this crystals. i don`t know either it salt or protein crystal . my protein has zero tryptophan so i could distinguish by UV camera. the condition was conditions: 0.1M SPG buffer pH 8 and 25%PEG 1500. in addition to Nickle chlorid 1mM. best regards Amr
