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Effect of Neuraminidase on -casein

Eastern Regional Research Laboratory², Philadelphia 18, Pennsylvania

ABSTRACT

Interest in sialic acid (N-Acetyl Neuraminic Acid, NANA) has extended into the field of milk protein chemistry. This carbohydrate has been identified as a constituent of human milk oligosaccharides and appears in dialysates of bovine colostrum (4). NANA appears in the glyco-macropeptide (GMP) which is released from whole casein by the action of rennin (2, 7, 9), and exists in several minor protein fractions of bovine milk (11). Dumas and Alais (3) recently isolated, crystallized, and characterized NANA obtained from bovine casein.

The presence of strongly hydrophilic NANA in -casein (1) has prompted us to determine the possible role of this carbohydrate in the stabilization of _s-casein in the presence of Ca⁺⁺. This paper reports the effects of neuraminidase (NANAse) on the release of NANA from -casein and its effect on the stabilizing power of -casein.

-Casein was prepared by the improved method of McKenzie and Wake (8). The -casein obtained by this method was essentially free of contamination in starch-gel-urea electrophoresis (8), possessed an S₂₀ of 14 at pH 6.98, T/2 = 0.20 in the phosphate buffer of Waugh and von Hippel (15), and was excellent stabilizer of _s-casein in the presence of Ca⁺⁺.

² Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.