Isoelectric points of proteins, determined by isoelectric focusing in the presence of urea and ethanol

Isoelectric points, pIapp, in sucrose-urea-water and glycerol-ethanol-water mixtures and isoelectric points, pI, in water have been determined at 25° for some carrier ampholytes. The differences, pIapp---pI, are shown to account for the primary medium effect and the pH measuring cell effect on the isoelectric point. The diferences, pIapp---pI, for Ampholines are used to correct apparent isoelectric points of proteins. pI shifts resulting from the denaturing effect of urea and ethanol are discussed in terms of the conformation change