Selective precipitation of proteins from guanidine hydrochloride-containing solutions with ethanol

The solubility of guanidine hydrochloride in ethanol and conversely the low solubility of proteins have been used as the basis for a procedure for recovering proteins from guanidine-containing solutions by selective precipitation. Yields of greater than 94% were observed with as little as 28 ng protein and of 98% for larger quantities of protein up to 20 mg/ml. The precipitations were independent of molecular weight for proteins in the range of 6-100 kDa and could be run in as little as 5 min at room temperature. Unlike the conventional desalting methods for removing guanidine, ethanol precipitation is rapid, efficient, and can be applied simultaneously to a large number of samples. The approach should have a wide range of applications.