Nomenclature of the Proteins of Bovine Milk—First Revision

Abstract

Summary The α-casein component of the casein system of milk, which appears as a single, leading electrophoretic peak at pH 8.6, is heterogeneous and should he referred to as the α-casein fraction. The components comprising this fraction vary in distribution, dependent upon the experimental conditions. Alpha -casein has been separated into calcium-sensitive and calcium-insensitive fractions which have been designated by various symbols. These fractions usually are in the form of an α (Ca sensitive)—α (Ca insensitive) complex in equilibrium with its components. In view of the complexity of the α-casein fraction, this Committee feels that no recommendations on nomenclature should be made at this time. Cherbuliez's δ-casein, Hammersten's proteose, and the 2% and 12% TCA-soluble peptides of Alais and Nitschmann, materials apparently derived from α-casein by various procedures, are discussed in this report. β-lactoglobulin, obtained from mixed milk, is composed of at least two forms of β-lactoglobulin which are genetically determined and referred to as β-lactoglobulins A and B, discernible by paper electrophoresis in veronal buffer at pH 8.6, where Type A constitutes the leading component. Further, Type A associates in acetate buffer between pH 3.7 and 5.2 and is essentially monomeric at pH values alkaline to its isoelectric point, whereas Type B exists in its monomeric form under similar conditions. These characteristics explain in part the electrophoretic and ultracentrifugal heterogeneity of normal (mixed) β-lactoglobulins A + B and β-lactoglobulin A .