Membranes of Mammary Gland. VI. Lipid and Protein Composition of Golgi Apparatus and Rough Endoplasmic Reticulum from Bovine Mammary Gland

Abstract

The lipid and protein composition of Golgi apparatus and rough endoplasmic reticulum fractions from bovine mammary gland was determined and compared with plasma membrane and milk fat globule membrane fractions. Golgi apparatus was intermediate between endoplasmic reticulum and the plasma membrane-globule membrane with respect to content of lipid phosphorus, cholesterol, protein bound sialic acid, cerebrosides, phosphatidyl choline and sphingomyelin. Fatty acid composition of total polar lipids and individual phospholipids were similar if not identical among all membrane fractions. Membrane fractions washed by procedures which remove adsorbed and intraluminal (secretory) proteins had similar polyacrylamide gel electrophoretic patterns. Endoplasmic reticulum, Golgi apparatus, and milk fat globule membrane had eight electrophoretically identical protein bands. Molecular weights of membrane proteins ranged from 11,500 to 102,000. Washed endoplasmic reticulum, Golgi apparatus and milk fat globule membrane fractions had similar amino acid compositions. These results are consistent with the hypothesis of Golgi apparatus-mediated endomembrane differentiation. The interrelation between lipid and protein and lactose secretion is discussed. © 1972, American Dairy Science Association. All rights reserved.