Multiple overlapping salt lattices can sometimes look like protein diffraction, as long as you're looking in only two dimensions. However, if you can find the dominant rings, you should be able to discriminate since the c-spacing of salt would nearly always be pretty small. Consider powder patterns, and you should see what I mean.
Generally speaking, if your crystals visually appear to be single, and give huge salt peaks - then they're probably salt. Exceptions - large, non-diffracting protein crystals that have small salt crystals stuck to them. Ultimately, you can use the 'stick a fork in it' method: stick a needle in your rod-like crystals and push. If you hear a crack, and see sharp clean edges on the break - it's salt. If you feel the crystal 'give' and see bending or pitting - it's probably protein. Good luck! Artem > Hi All! > > I have been trying to screen for my protein crystals, from the > crystals grown in 0.5 M Ammonium Sulphate, 1.0M Lithium Sulphate > Monohydrate in 0.1 M TriSodium Citrate Buffer dihydrate Buffer at pH 5.6. > Two different kinds of crystals observed: rod shaped and thin platy > ones. Whenever I am trying to collect data from the rod shaped ones I am > getting dominantly salt patterns but also spots at 15 A resolution bin > repeatedly, where some of the spots very much look like from protein! > what can be the reason for this? if anyone has come across similar > situation please help. > > with regards, > Sreeram Mahesh > > > Research Student > Prof S Ramakumar's lab > PHYSICS department > IISc Bangalore-560 012. > ph:080-2293 2718. > mobile: 9241145183. > > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. >
