conformation changed after lyophilizatin - (Jul/28/2004 )

Hi:
I have purified the histag protein from E.Coil. The purity is perfect, more than 98%,checked by Mass. But now I found a very strange things that the CD spectrum was different with other peoples data. And I measured the CD spectrum just before I did lyophilization. It is different with after lyophiliation but similar with others.
What happened during the lyophilization? Tris-tricin shows no any change after lyophilization!
Thanks in advance!

That's an interesting question and it has to do with thermodynamics. To put it in a nutshell, proteins (most of them) have two denaturation (or melting) temperatures. One around 40-50C and the other around 0-5C or less, which is what we call cold denaturation. Usually the protein will recover its native structure after freeze/thawing, but it's possible in your case that the cold denaturation caused by pre-lyophilization freezing might be irreversible. Hence, you should avoid lyophilization.