Biochemical and Morphological Comparison of Plasma Membrane and Milk Fat Globule Membrane From Bovine Mammary Gland

Abstract

Purified plasma membrane fractions from lactating bovine mammary glands and membranes of milk fat globules from the same source were similar in distribution and fatty acid composition of phospholipids. The sphingomyelin content of the phospholipid fraction of both membranes was higher than in these fractions from other cell components, ß-carotene, a constituent characteristic of milk fat, was present in the lipid fraction of the plasma membrane. Cholesterol esters of plasma membrane were similar in fatty acid composition to those of milk fat globule membranes. Disc electrophoresis of either membrane preparation on polyacrylamide gels revealed a single major protein component characteristic of plasma membrane from other sources. Distinct morphological differences between plasma membrane and milk fat globule membranes were observed in both thin sections and in negatively stained material. Plasma membrane was vesicular in appearance while milk fat globule membranes had a platelike aspect. These observations are consistent with derivation of fat globule membrane from plasma membrane accompanied by structural rearrangement of membrane constituents.

Purification and characterisation of a breast-cancer-associated glycoprotein not expressed in normal breast and identified by monoclonal antibody 83D4

“…Preparation of human milk fat globule membanes (HMFGM) Crude HMFGM were prepared from fresh human milk as described (Keenan et al, 1970). After centrifugation at 100,000g for 1 h, the HMFGM pellet was resuspended in PBS 0.5% NP40, containing protease inhibitors.…”

Intracellular Origin of Milk Fat Globules and the Nature of the Milk Fat Globule Membrane

“…Well-characterized apical plasma membrane preparations from mammary gland have not been forthcoming; preparations of plasma membranes from this source are enriched in baso-lateral membrane fragments and may contain plasma membranes from other cell types (Keenan et al, 1970. Nevertheless, comparisons of plasma membranes isolated from mammary gland with MFGM show these membranes to be similar in polar lipid composition and some protein constituents (Keenan et al, 1970. Secretory vesicles from the mammary gland are osmotically fragile and have proven diYcult to isolate.…”

Improvement in the Immunological Methods for the Detection of Human Breast Carcinomas

“…The measurement of a-lactalbumin in plasma by radioimmunoassay is un reliable due to the presence of a population of naturally occurring antibodies to bovine lactalbumin in the blood of many individuals [Woods et al, 1979], Even when this problem is overcome, its assay in serum does not seem to be of clinical value in breast carcinomas [Woods et al, 1979], Another important constituent of the breast milk is the milk fat globule membrane (MFGM) which has been less extensively studied in relation to breast car cinomas. The fat globules in milk are surrounded by a membrane which is derived from the plasma membrane of mammary secretory epithelia at the time of milk secretion [Keenan et al, 1970;Wooding, 1971a, b]. Thus, the membrane constituents of the milk fat globule provide an important source of material for investiga tion.…”