Se. Szedlacsek et al., ESTERIFICATION OF OXYSTEROLS BY HUMAN PLASMA LECITHIN-CHOLESTEROL ACYLTRANSFERASE, The Journal of biological chemistry, 270(20), 1995, pp. 11812-11819
In the present study, lecithin-cholesterol acyltransferase (LCAT) cata
lyzed esterification of oxysterols was investigated by using discoidal
bilayer particles (DBP) containing various oxysterols, phosphatidylch
olines, and apolipoprotein A-I. The esterified oxysterols were analyze
d by high pressure liquid chromatography, gas chromatography, and mass
spectrometry. LCAT esterified all oxysterols tested that are known to
be present in human plasma. The esterification yields in almost all c
ases were relatively high, often as high as the yield of cholesterol e
sterification. When DBP preparations containing 27-hydroxycholesterol
and various phosphatidylcholines were used for the LCAT reaction, both
monoesters and diesters were produced. The mass spectrometry analysis
showed that the monoester was produced by the esterification of the 3
beta-hydroxyl group and not the 27-hydroxyl group. The diesters were
apparently produced by the esterification of the 27-hydroxyl group onl
y after the esterification of the 3 beta-hydroxyl group. Phosphatidylc
holine containing a saturated acyl group at sn-1 position and an unsat
urated acyl group at sn-2 position gave generally high esterification
yield. The esterification of various oxysterols was compared by using
DBP containing dioleoyl-phosphatidylcholine and individual oxysterols.
All oxysterols produced 3 beta-oleoyl monoesters, Unlike 27-hydroxych
olesterol, 25-hydroxycholesterol, 7 alpha-hydroxycholesterol, 7 beta-h
ydroxycholesterol, or cholestanetriol did not produce diesters. Variou
s factors influencing the formation of the monoesters and diesters fro
m 27-hydroxycholesterol were investigated. When dioleoyl-phosphatidylc
holine was used as the acyl donor, prolonged dialysis of DBP preparati
ons and increase in the ratio of the enzyme concentration to substrate
particle concentration increased the diester formation. Significant a
mounts of diesters were also produced by using 1-palmitoyl-2-oleoyl-ph
osphatidylcholine and other phosphatidylcholines as the acyl donors. B
y analyzing the conditions of monoester and diester formation, a schem
e for the LCAT reaction pathway was proposed.