Charge forms of Wistar rat alpha-lactalbumin. A contradiction.

alpha-Lactalbumin was purified from the milk of Wistar rats and was compared to that obtained from Fisher 344 rats. alpha-Lactalbumin isolated from the Wistar rat exists as two forms which differ in their sialic acid content, as the desialyated forms migrate to one identical position on polyacrylamide gels. These two charge forms are identical with the charge Forms II and III previously characterized from Fisher rat alpha-lactalbumin. No evidence was found to verify previous reports that one form of the Wistar rat alpha-lactalbumin had a higher molecular weight than the other form. Indeed, the molecular weights and the amino acid compositions of the two forms of Wistar rat alpha-lactalbumin are identical. In addition, the partial amino acid sequence at the NH2-terminal end and the amino acid composition of the COOH-terminal cyanogen bromide peptide of the two forms are identical. The results in this study contradict those reported previously and show that rat alpha-lactalbumin exists as a single molecular weight species.