Correction of the anomalous electrophoretic behavior of ribonuclease A

Ribonuclease A behaves anomalously on polyacrylamide gel electrophoresis at acid pH. The distance traveled by the protein is a function of the amount of enzyme added at the lower range of detectable activity (10 pg to 100 ng). Addition of myoglobin (1 mg/ml) abolishes the anomaly. The observations are consistent with the known affinity of RNase for anions. Caution is warranted in the interpretation of apparent electrophoretic variants of RNase observed at low concentrations of enzyme.