I am working with rhizome proteins i extract using a phenol based method. The proteins have given me good SDS PAGE bands. My problem now is that my proteins of late seem to be insoluble in urea lysis buffer (7M urea, 2M thiourea, 2% chaps) after hours of vortexing. Sometimes the proteins dissolve and i keep the solutin at -20C. Upon thawing, the proteins tend to precipita. I was planning to go to IEF and 2D electrophoresis, but with the problems i have highlighted, i am very worried. Please help me.