Assembly and Secretion of the Lipid Globules of Milk

  • Thomas W. Keenan
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 501)


While the structure, biosynthesis, processing, and nutritional characteristics of milk lipids have been studied extensively, remarkably little is known about the intracellular formation of triacylglycerol-rich droplets destined to be secreted as milk lipid globules. That lipid droplets are secreted from cells by progressive envelopment in plasma membrane has been recognized since the pioneering electron microscope study of Bargmann and Knoop (1959); but what molecules and forces are involved in this secretory process remains a matter of speculation. That there has been little study of the lipid globule secretion mechanism is surprising for a number of reasons: This secretion mechanism involves large losses of differentiated regions of plasma membrane from the cell; this membrane can be obtained readily for study; the cells must have an efficient mechanism for replenishment of the secreted plasma membrane. This lipid secretory mechanism may be unique to mammary epithelial cells, as this pathway has not been described for any other cell type. There are striking parallels between lipid droplet secretion and the release of enveloped viruses from cells(reviews, Patton & Keenan 1975; Mather & Keenan 1983; Keenan et al. 1988). Of the several reasons that can explain this lack of study, two emerge as primary. One is that many of the agencies providing support for studies of milk have had ultimate commercial utilization as their overriding interest. Fundamental biological questions regarding the origin of milk lipid globules have not been within this sphere of interest. Second.


Lipid Droplet Mammary Epithelial Cell Microsomal Triglyceride Transfer Protein Lipid Globule Cytoplasmic Lipid Droplet 
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Copyright information

© Springer Science+Business Media New York 2001

Authors and Affiliations

  • Thomas W. Keenan
    • 1
  1. 1.Department of BiochemistryVirginia Polytechnic Institute and State UniversityBlacksburg

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