Summary
Whether both casein and noncasein (serum or whey) proteins of milk are contained within the same secretory vesicles of milk secreting mammary epithelial cells was explored. Antibodies to a major casein and to α-lactalbumin of rat milk were localized in thin sections with colloidal gold-conjugated second antibodies. Antibodies to the casein component bound to an antigen present within lumina of Golgi apparatus cisternae and within secretory vesicles. This antigen was also recognized in structures within secretory vesicles and within alveolar lumina which were ultrastructurally identified as casein micelles. Antigens recognized by antibodies to α-lactalbumin also were present in Golgi apparatus cisternae and within secretory vesicles. Both anti-casein and anti-α-lactalbumin antibodies recognized antigens within the same secretory vesicles. These observations show that one major noncasein protein of rat's milk is present in casein-containing secretory vesicles.
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Shappell, N.W., Dylewski, D.P. & Keenan, T.W. Colocalization of α-lactalbumin and a major casein in secretory vesicles of rat mammary epithelial cells. Protoplasma 135, 112–118 (1986). https://doi.org/10.1007/BF01277004
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DOI: https://doi.org/10.1007/BF01277004