Title page for ETD etd-11142012-040236


Type of Document Master's Thesis
Author Deeney, Jude T.
URN etd-11142012-040236
Title Micro lipid droplet precursors of milk lipid globules
Degree Master of Science
Department Biochemistry and Nutrition
Advisory Committee
Advisor Name Title
Keenan, Thomas W. Committee Chair
Bevan, David R. Committee Member
Gregory, Eugene M. Committee Member
Smith, David F. Committee Member
Keywords
  • Milkfat
Date of Defense 1985-01-05
Availability restricted
Abstract
The lipid in milk (milk fat) is found in the form of droplets

known as milk lipid globules (MLG). These milk lipid globules are

encompassed by a unit membrane known as the milk lipid globule

membrane (MLGM) which is derived from the apical plasma membrane of

the mammary epithelial cell during secretion. In lactating mammary

epithelial cells, immediate precursors of milk lipid globules appear

to be cytoplasmic lipid droplets (CLD). These cytoplasmic lipid

droplets have diameters >l μm and are characterized by an electron

dense, granular surface coat. A previously unrecognized group of

structures with diameters <.5 μm, which resemble cytoplasmic lipid

droplets in matrix and surface coat appearance, has been observed.

The surface coat of these triacylglycerol containing structures,

termed micro lipid droplets (μLD), was similar to that of cytoplasmic

lipid droplets in enzyme and polypeptide composition. Morphological

evidence suggested that these small structures may originate from

rough endoplasmic reticulum (RER) and fuse with cytoplasmic lipid

droplets. Immunochemical studies showed homology of certain proteins

among the rough endoplasmic reticulum, micro lipid droplets and

cytoplasmic lipid droplets, which supported the possibility of an endoplasmic reticulum origin of these droplets. The rate of

incorporation of [l—l4C]—palmitate and [1,2,3-3H]—glycerol into

lipid of RER, μLD, CLD and MIG fractions suggested a possible

translocation pathway of triacylglycerols from the rough endoplasmic

reticulum to cytoplasmic lipid droplets. The micro lipid droplets

seem to provide triacylglycerols to support growth of cytoplasmic

lipid droplets. In addition, morphological evidence suggested that

these micro lipid droplets can be secreted directly in a manner

similar to cytoplasmic lipid droplets, providing for the small lipid

globules in milk. Little is known concerning the biochemical processes

of milk lipid secretion but it is thought that butyrophilin, a

glycoprotein found in milk lipid globule membrane, may play a role.

After treatment of mammary epithelial cells with tunicamycin,

butyrophilin content of this membrane is reduced. Thus a method for

the study of the physiological role of this glycoprotein is proposed.

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