Apparent anomalies in the resolution of cytochrome P-450 isoenzymes by gel electrophoresis.

Cytochromes P-450b and P-450e are two phenobarbital-inducible rat hepatic microsomal isoenzymes that possess approx. 97% sequence homology and show apparent anomalous behaviour in SDS-PAGE and isoelectric-focusing under denaturing conditions. Although the two enzymes differ in Mr by less than 0.1% and possess no apparent net charge difference, then can be resolved in both electrophoretic systems. These apparent discrepancies are discussed in terms of the predicted secondary structure of the proteins and the potential for certain specific amino acid substitutions to cause anomalous behaviour in SDS-PAGE. The results of electrophoresis of these cytochrome P-450 isoenzymes indicate that much smaller differences in primary structure can be detected by these methodologies than would be predicted from theoretical considerations.