The sensitivity of isoelectric focusing and electrophoresis in the detection of sequence differences in proteins.

Fourteen myoglobins of known sequence were examined by isoelectric focusing with and without urea. The 14 sequences formed six distinct mobility classes on gels without urea and three classes on those with urea. For these proteins, isoelectric focusing provides no advantage over single, nonequilibrium, nondenaturing gels in the total number of distinguishable mobility classes. Only major charge differences, resulting from the changes in the total numbers of acidic and basic amino acids, can be detected on gels with urea, indicating that denaturation by urea alters proteins so that small differences in ionization are eliminated.