A. Lopezcandales et al., CHOLESTEROL TRANSPORT FUNCTION OF PANCREATIC CHOLESTEROL ESTERASE - DIRECTED STEROL UPTAKE AND ESTERIFICATION IN ENTEROCYTES, Biochemistry, 32(45), 1993, pp. 12085-12089
We have recently hypothesized that neutral lipids can, in part, move a
cross biological membranes via a mechanism involving enzymes anchored
to membrane proteoglycans such as those found in the brush border of t
he enterocyte [Bosner, M. S., Gulick, T., Riley, D. J. S., Spilburg, C
. A., & Lange, L. G. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7438-744
2]. Present results now show a subsequent, essential protein-mediated
sorting of neutral lipids for further intracellular metabolism. Thus,
in the absence of enzyme, 0.002 pmol of cellular ester appeared after
2 h, and its level increased only 3.5-fold after 12 h. However, in the
presence of cholesterol esterase, the level of cholesterol ester incr
eased 39-fold in the same time period, indicating that the enzyme-medi
ated uptake accounts for 10-fold greater ester synthesis than that fro
m basal absorption. Kinetic analysis reveals that both enzyme-mediated
and background absorption depend on taurocholate concentration and ar
e second-order reactions more likely dependent on collision than diffu
sion. Other lipid-recognizing proteins such as pancreatic triglyceride
lipase and the intestinal fatty acid binding protein are not stimulat
ory to intracellular cholesterol processing. Taken together, these dat
a suggest that pancreatic cholesterol esterase and possibly other prot
eoglycan-binding extracellular enzymes of neutral lipid metabolism may
facilitate movement of neutral lipids into the plasma membrane and di
rect them into functional intracellular sites.