Minor components of bovine -lactalbumin A and B

Bovine α-lactalbumin B consists of one major and three minor components. They have been designated in terms of their decreasing order of mobility in starch gel electrophoresis at pH 7.7: α-lactalbumin B fast component (Component F), α-lactalbumin B major component (Component M), α-lactalbumin B slow component 1 (Component S1) and α-lactalbumin B slow component 2 (Component S2). Component F is eluted with Component M in chromatography on Sephadex G-75 at pH 6.3; whereas Components S1 and S2 are eluted together, but ahead of Component M. The order of elution from DEAE-Sephadex at pH 6.3–7.9 is Component S2, S1, M and F. These properties are exploited to separate the components. It is demonstrated that the minor components are true components, not resulting from interaction effects or conformational change. All are active in the lactose synthetase system, and have the same amino acid composition as the major component. Component F possibly differs from Component M in having one less amide group. Components S1 and S2 have carbohydrate moieties. The number of residues in Component S1 are 6–7 hexosamine, 6 hexose, 1 6-deoxyhexose, 1 sialic acid. Component S2 has the same number, except it has no sialic acid. The A variant has analogous minor components. Thus the AB heterozygote consists of 2 major and 6 minor components.