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Enzymic characteristics of fat globule membranes from bovine colostrum and bovine milk

Title: Enzymic characteristics of fat globule membranes from bovine colostrum and bovine milk
Authors: Powell, JT
Järlfors, U
Brew, K
Item Type: Journal Article
Abstract: Fat globule membranes have been isolated from bovine colostrum and bovine milk by the dispersion of the fat in sucrose solutions at 4 degrees C and fractionation by centrifugation through discontinuous sucrose gradients. The morphology and enzymic characteristics of the separated fractions were examined. Fractions comprising a large proportion of the total extracted membrane were thus obtained having high levels of the Golgi marker enzymes UDP-galactose N-acetylglucosamine beta-4-galactosyltransferase and thiamine pyrophosphatase. A membrane-derived form of the galactosyltransferase has been solubilized from fat and purified to homogeneity. This enzyme is larger in molecular weight than previously studied soluble galactosyltransferases, but resembles in size the galactosyltransferase of lactating mammary Golgi membranes. In contrast, when fat globule membranes were prepared by traditional procedures, which involved washing the fat at higher temperatures, before extraction, galactosyltransferase was not present in the membranes, having been released into supernatant fractions, When the enzyme released by this procedure was partially purified and examined by gel filtration, it was found to be of a degraded form resembling in size the soluble galactosyltransferase of milk. The release is therefore attributed to the action of proteolytic enzymes. Our observations contrast with previous biochemical studies which suggested that Golgi membranes do not contribute to the milk fat globule membrane. They are, however, consistent with electron microscope studies of the fat secretion process, which indicate that secretory vesicle membranes, derived from the Golgi apparatus, may provide a large proportion of the fat globule membrane.
Issue Date: 1-Mar-1977
Date of Acceptance: 1-Mar-1977
URI: http://hdl.handle.net/10044/1/41185
DOI: http://dx.doi.org/10.1083/jcb.72.3.617
ISSN: 1540-8140
Publisher: Rockefeller University Press
Start Page: 617
End Page: 627
Journal / Book Title: Journal of Cell Biology
Volume: 72
Issue: 3
Copyright Statement: © 1977 Rockefeller University Press
Keywords: Animals
Golgi Apparatus
Lactose Synthase
N-Acetyllactosamine Synthase
Thiamine Pyrophosphatase
Developmental Biology
06 Biological Sciences
11 Medical And Health Sciences
Publication Status: Published
Appears in Collections:Department of Surgery and Cancer