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乳脂球膜蛋白英文综述


The Progress in the Milk Fat Globule Membrane
Abstract: Butyrophilin, XOR and the surface growth factor8 of the milk fat
globule are the three kinds of major membrane proteins of milk fat globule membrane. This review focuses on current research relating to the composition and structure of MFGM, and interactions of MFGM with skim milk proteins during heat treatments [1]. Various methods of isolating MFGM, reported in the literature, are reviewed and evaluated for their potential to produce MFGM ingredients for food applications[2]. Keywords: Fat globules; Milk fat globule membrane; MFGM proteins

Introduction
Many properties of dairyproducts, e.g. their stability and acceptability, aredetermined by the responses of the MFGM componentsto these treatments.Thus, an understanding of this unique membrane systemis important for producing dairy products with consistentproperties[3]. The natural fat globules in milk are coated with aprotective layer generally known as the milk fat globulemembrane (MFGM). Milk fat is a major component of milk,the content is generally accounted for 3% to 5%,and the flavor of milk plays an important influence. Milk fat to Dispersed in the form of fat globules in the milk was observed under a microscope for the ball Sphercal or elliptical shape, the surface is covered with a film of 5~10nm[4].The MFGM is closely involved innatural processes in milk (e.g. creaming and agglutination)and is markedly affected by treatments, such ascooling, heating, and homogenization of dairy products[5].

1. Composition and structure of MFGM
The amount and the composition of MFGM can vary considerably depending on both the fat content and the fat globule size, which are, in turn, affected by several factors, such as diet, breed, health and stage of lactation of cows. For instance, small fat globules, because of their large surface area, account for a large proportion of the total MFGM material. In addition, milk handling procedures during and after milk harvesting, e.g.aging, agitation, air inclusion, temperature changes and heat treatments, may affect the composition of MFGM[6]. The total mass of fat globules that is accounted for by membrane material has not been determined with certainty. An estimated mass of the membrane is 2 –6% of that of the total fat globules. Proteins and phospholipids together account for over 90% of the membrane dry weight, but the relative proportions of lipids and proteins may vary

widely. The membrane consists of complex mixtures of proteins, phospholipids, glycoproteins, triglycerides, cholesterol, enzymes and other minor components. Protein accounts for 25 –60% of the mass of the membrane material, depending upon the isolation method chosen and the sample history. Historically, polyacrylamide gel electrophoresis had been used to elucidate the protein composition of the MFGM and major MFGM proteins were designated according to their relative mobility in sodium dodecyl sulfate SDS-PAGE and their ability to stain with Coomassie blue or the glycoprotein-specific periodic acid/Schiff reagent.A classification scheme that specifies the mobility, molecular weight and staining characteristics of different proteins and the gel system used, recommended by the Milk Protein Nomenclature Committee, is now widely used. Over 40 MFGM proteins can be resolved using a combination of electrophoresis and isoelectric focusing, and several of these proteins have been isolated and characterized by sequence analysis or the corresponding cDNAs[7]. The major proteins resolved in order from the top of SDS gels are the mucin MUC 1, the redox enzyme xanthine oxidase/ dehydrogenase, a glycoprotein PAS III, butyrophilin, glycosylated variants of periodic acid/Schiff, PAS 6/7, adipophilin and nfatty acid binding protein. Butyrophilin is a major glycoprotein of bovine MFGM and comprises over 40% by weight of the total protein associated with MFGM in milks from Holstein cows and approximately 20% in Jersey milk. In bovine milk, about 60% of the phospholipids are associated with fat globules and the rest are located in the membrane material of skim milk. Although the structure of MFGM is not known in detail, the arrangement of the constituents in MFGM has been well documented by a number of studies[8].

2. Functionmilk of fat globule membrane protein 2.1. Study of the main component
Due to the composition and nature of the MFGM proteins may have a great relationship with the secretion of milk fat, so there are many scholars have studied.Bruder et al (1982) by studying the topological structure of protein-protein interactions and protein 2 that MFGM protein into the inner layer is made butyrophilin (Btn) and xanthine oxidoreductase (XOR) components. B tn is the major protein component of bovine MFGM, 20% to 40% of the total membrane protein[9]. B tn expressed mainly in breast, enriched in plasma membrane, and the top of the milk fat globule membrane. Compared with the Btn, XOR is a soluble cytosolic enzyme, and are mainly concentrated in the milk-secreting cells of the inner cytoplasmic membrane, by forming a complex with the Btn involved in fat secretion[10]. Na ohito (1994) through the extraction of the MFGM molecules, to prepare a series of

monoclonal antibodies are cloned using c DNAs, the re-encoding bovine MFG 2E8, which is a polysaccharide found that the protein, inferred MFG2E8 is a membrane protein, and the butterfat secretion plays a process used[11]. 2.2. Btn and XOR Btn is a member of the Ig family, is only one kind of breast ? type transmembrane glycoprotein, high in lactating mammary gland The expression degree[12]. XOR dehydrogenase flavoprotein belonging to the molybdenum-containing family members, there are two identical subunits (molecular weight 147 kD), each subunit containing a molybdenum atom, a flavin adenine nucleotide (FAD), 2 different Fe / 2S2 center, there is a strong function of both the correlation of fat secretion process. Frank e et al (1981) by cloning the rat Btn found that some express their cells GST2f us ion protein (gold sodium thiosulfate fusion protein), with the reducing agent MFGM and XOR can find Btn from MF released from GM[13]. Mammary epithelial cells in culture can be the domain of the XOR Btn C2 terminus combined, XOR as a dimer can bind two Btn molecules, play a major role in the formation of molecular aggregates when the membrane structure, so that the Btn / XOR forming protein complexes may be formed in the core in combination with other accessory molecules of the initiator, which can be successfully wrapped in fat globules[15].

3. References
[1] Keenan TW, Dylewski DP. Intracellular origin of milk lipid globules and the nature of structure of milk fat globule membrane. In: Fox PF, editor. Advanced dairy chemistry Lipids, vol. 2. . London’Chapman & Hall, 1995. p. 89. [2] Mather IH, Keenan TW. Origin and secretion of milk lipids. J Mammary Gland Biol Neoplasia 1998;3:259-73. [3] Keenan TW. Milk lipid globules and their surrounding membrane: a brief history and perspectives for future research. J Mammary Gland Biol Neoplasia 2001;6:365-71. [4] Heid HW, Keenan TW. Intracellular origin and secretion of fat globules. Eur J

Cell Biol 2005;84:245–258. [5] McPherson AV, Kitchen BJ. Review of the progress of dairy science: the bovine milk fat globule membrane—its formation, composition, structure and behaviour in milk and dairy products. J Dairy Res 1983;50:107– 33. [6] Walstra P. Physical chemistry of milk fat globules. In: Fox PF, editor. Advanced dairy chemistry Lipids, vol. 2. London’ Chapman & Hall, 1995. p. 101. [7] Evers JM. The milk fat globule membrane—compositional and structural changes post secretion by the mammary secretory cell. Int Dairy J 2004;14:661–674. [8] Mather IH. A review and proposed nomenclature for major proteins of the milk fat globule membrane. J Dairy Sci 2000;83:203– 47.Excellent review of physio-chemical characteristics and structures of most MFGM proteins. A revised nomenclature is proposed for the major MFGM proteins. [9] Danthine S, Blecker C, Paquot M, Innocente N, Deroanne C. Progress in milk fat globule membrane research: a review. Lait 2000;80:209– 22. [10] Spicer AP, Duhig T, Chilton BS, Gendler SJ. Analysis of mammalian MUC1 genes reveals potential functionally important domains. Mamm Genome 1995;6:885– 8. [11] Huott ML, Josephson RV, Hens JR, Rogers GW, Patton S. Polymorphic forms of the epithelial mucin, PAS-I (MUC1), in milk of Holstein cows (Bos Taurus). Comp Biochem Physiol 1995;111B:559– 65. [12] Wand WR, Brady FO, Wiley RD, Rajagopalan KV. A new purification procedure for bovine milk xanthine oxidase: effect of proteolysis on the subunit structure. Arch Biochem Biophys 1975;169:695– 701. [13] Mather IH, Weber K, Keenan TW. Membranes of mammary gland: XII. Loosely associated proteins and compositional heterogeneity of bovine milk fat globule membrane. J Dairy Sci 1977;60:394– 402. [14] Mather I, Jack LJW. A review of the molecular and cellular biology of butyrophilin, the major protein of bovine milk fat globule membrane. J Dairy Sci 1996;76:3832–50. [15] Mondy BL, Keenan TW. Butyrophilin and xanthine oxidase occur in constant molar proportions in milk lipid globule membrane but vary in amount with

breed and stage of lactation. Protoplasma 1993;177: 32–36. One of the first papers demonstrating the existence of complexes between butyrophilin and xanthine oxidase.


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