Journal of Lipid Research, Vol 26, 964-969, Copyright © 1985 by Lipid Research, Inc.
Coupling of photoactivatable glycolipid probes to apolipoproteins A-I and A-II in human high density lipoproteins 2 and 3
TA Berkhout, PH Groot, R van Belzen and KW Wirtz
High density lipoprotein (HDL) from human serum was subfractionated into
HDL2 and HDL3 by rate-zonal density gradient ultracentrifugation. The
orientation of apoproteins (apo) A-I and A-II in these subfractions was
investigated by use of the photosensitive glycolipid probes, 2-(4-
azido-2-nitrophenoxy)-palmitoyl[1-14C]glucosamine (compound A) and 12-
(4-azido-2-nitrophenoxy)-stearoyl[1-14C]glucosamine (compound B). Both
probes were added to the HDL-structures in a ratio of two or three probe
molecules per particle and were photoactivated by irradiation at a
wavelength above 340 nm. After delipidation the probe-apoprotein adducts
were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
Both the "shallow" probe (compound A) and the "depth" probe (compound B)
were coupled for 10-14% (of the label added) to apoA- I and apoA-II from
HDL3 and for about 6% to apoA-I and apoA-II from HDL2. By taking into
account the relative amounts of apoA-I and apoA- II, it was estimated that
the "shallow" probe labeled apoA-I 40% more effectively than apoA-II in
both HDL2 and HDL3; the "depth" probe labeled apoA-I and apoA-II equally
well in both subfractions. The data suggest that towards the surface HDL2
and HDL3 contain a relatively larger portion of apoA-I than apoA-II, whilst
towards the core both subfractions are occupied by an equal portion of
apoA-I and apoA-II. Application of these photolabels has failed to point
out differences in the structural organization of HDL2 and HDL3.